/*
 * Intel(R) Trace Hub Memory Storage Unit
 *
 * Copyright (C) 2014-2015 Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 */

#define pr_fmt(fmt)     KBUILD_MODNAME ": " fmt

#include <linux/types.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <linux/sizes.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/io.h>
#include <linux/dma-mapping.h>

#include <asm/cacheflush.h>

#include "intel_th.h"
#include "msu.h"

#define msc_dev(x) (&(x)->thdev->dev)

/**
 * struct msc_block - multiblock mode block descriptor
 * @bdesc:      pointer to hardware descriptor (beginning of the block)
 * @addr:       physical address of the block
 */
struct msc_block {
        struct msc_block_desc   *bdesc;
        dma_addr_t              addr;
};

/**
 * struct msc_window - multiblock mode window descriptor
 * @entry:      window list linkage (msc::win_list)
 * @pgoff:      page offset into the buffer that this window starts at
 * @nr_blocks:  number of blocks (pages) in this window
 * @block:      array of block descriptors
 */
struct msc_window {
        struct list_head        entry;
        unsigned long           pgoff;
        unsigned int            nr_blocks;
        struct msc              *msc;
        struct msc_block        block[0];
};

/**
 * struct msc_iter - iterator for msc buffer
 * @entry:              msc::iter_list linkage
 * @msc:                pointer to the MSC device
 * @start_win:          oldest window
 * @win:                current window
 * @offset:             current logical offset into the buffer
 * @start_block:        oldest block in the window
 * @block:              block number in the window
 * @block_off:          offset into current block
 * @wrap_count:         block wrapping handling
 * @eof:                end of buffer reached
 */
struct msc_iter {
        struct list_head        entry;
        struct msc              *msc;
        struct msc_window       *start_win;
        struct msc_window       *win;
        unsigned long           offset;
        int                     start_block;
        int                     block;
        unsigned int            block_off;
        unsigned int            wrap_count;
        unsigned int            eof;
};

/**
 * struct msc - MSC device representation
 * @reg_base:           register window base address
 * @thdev:              intel_th_device pointer
 * @win_list:           list of windows in multiblock mode
 * @nr_pages:           total number of pages allocated for this buffer
 * @single_sz:          amount of data in single mode
 * @single_wrap:        single mode wrap occurred
 * @base:               buffer's base pointer
 * @base_addr:          buffer's base address
 * @user_count:         number of users of the buffer
 * @mmap_count:         number of mappings
 * @buf_mutex:          mutex to serialize access to buffer-related bits

 * @enabled:            MSC is enabled
 * @wrap:               wrapping is enabled
 * @mode:               MSC operating mode
 * @burst_len:          write burst length
 * @index:              number of this MSC in the MSU
 */
struct msc {
        void __iomem            *reg_base;
        struct intel_th_device  *thdev;

        struct list_head        win_list;
        unsigned long           nr_pages;
        unsigned long           single_sz;
        unsigned int            single_wrap : 1;
        void                    *base;
        dma_addr_t              base_addr;

        /* <0: no buffer, 0: no users, >0: active users */
        atomic_t                user_count;

        atomic_t                mmap_count;
        struct mutex            buf_mutex;

        struct list_head        iter_list;

        /* config */
        unsigned int            enabled : 1,
                                wrap    : 1;
        unsigned int            mode;
        unsigned int            burst_len;
        unsigned int            index;
};

static inline bool msc_block_is_empty(struct msc_block_desc *bdesc)
{
        /* header hasn't been written */
        if (!bdesc->valid_dw)
                return true;

        /* valid_dw includes the header */
        if (!msc_data_sz(bdesc))
                return true;

        return false;
}

/**
 * msc_oldest_window() - locate the window with oldest data
 * @msc:        MSC device
 *
 * This should only be used in multiblock mode. Caller should hold the
 * msc::user_count reference.
 *
 * Return:      the oldest window with valid data
 */
static struct msc_window *msc_oldest_window(struct msc *msc)
{
        struct msc_window *win;
        u32 reg = ioread32(msc->reg_base + REG_MSU_MSC0NWSA);
        unsigned long win_addr = (unsigned long)reg << PAGE_SHIFT;
        unsigned int found = 0;

        if (list_empty(&msc->win_list))
                return NULL;

        /*
         * we might need a radix tree for this, depending on how
         * many windows a typical user would allocate; ideally it's
         * something like 2, in which case we're good
         */
        list_for_each_entry(win, &msc->win_list, entry) {
                if (win->block[0].addr == win_addr)
                        found++;

                /* skip the empty ones */
                if (msc_block_is_empty(win->block[0].bdesc))
                        continue;

                if (found)
                        return win;
        }

        return list_entry(msc->win_list.next, struct msc_window, entry);
}

/**
 * msc_win_oldest_block() - locate the oldest block in a given window
 * @win:        window to look at
 *
 * Return:      index of the block with the oldest data
 */
static unsigned int msc_win_oldest_block(struct msc_window *win)
{
        unsigned int blk;
        struct msc_block_desc *bdesc = win->block[0].bdesc;

        /* without wrapping, first block is the oldest */
        if (!msc_block_wrapped(bdesc))
                return 0;

        /*
         * with wrapping, last written block contains both the newest and the
         * oldest data for this window.
         */
        for (blk = 0; blk < win->nr_blocks; blk++) {
                bdesc = win->block[blk].bdesc;

                if (msc_block_last_written(bdesc))
                        return blk;
        }

        return 0;
}

/**
 * msc_is_last_win() - check if a window is the last one for a given MSC
 * @win:        window
 * Return:      true if @win is the last window in MSC's multiblock buffer
 */
static inline bool msc_is_last_win(struct msc_window *win)
{
        return win->entry.next == &win->msc->win_list;
}

/**
 * msc_next_window() - return next window in the multiblock buffer
 * @win:        current window
 *
 * Return:      window following the current one
 */
static struct msc_window *msc_next_window(struct msc_window *win)
{
        if (msc_is_last_win(win))
                return list_entry(win->msc->win_list.next, struct msc_window,
                                  entry);

        return list_entry(win->entry.next, struct msc_window, entry);
}

static struct msc_block_desc *msc_iter_bdesc(struct msc_iter *iter)
{
        return iter->win->block[iter->block].bdesc;
}

static void msc_iter_init(struct msc_iter *iter)
{
        memset(iter, 0, sizeof(*iter));
        iter->start_block = -1;
        iter->block = -1;
}

static struct msc_iter *msc_iter_install(struct msc *msc)
{
        struct msc_iter *iter;

        iter = kzalloc(sizeof(*iter), GFP_KERNEL);
        if (!iter)
                return ERR_PTR(-ENOMEM);

        mutex_lock(&msc->buf_mutex);

        /*
         * Reading and tracing are mutually exclusive; if msc is
         * enabled, open() will fail; otherwise existing readers
         * will prevent enabling the msc and the rest of fops don't
         * need to worry about it.
         */
        if (msc->enabled) {
                kfree(iter);
                iter = ERR_PTR(-EBUSY);
                goto unlock;
        }

        msc_iter_init(iter);
        iter->msc = msc;

        list_add_tail(&iter->entry, &msc->iter_list);
unlock:
        mutex_unlock(&msc->buf_mutex);

        return iter;
}

static void msc_iter_remove(struct msc_iter *iter, struct msc *msc)
{
        mutex_lock(&msc->buf_mutex);
        list_del(&iter->entry);
        mutex_unlock(&msc->buf_mutex);

        kfree(iter);
}

static void msc_iter_block_start(struct msc_iter *iter)
{
        if (iter->start_block != -1)
                return;

        iter->start_block = msc_win_oldest_block(iter->win);
        iter->block = iter->start_block;
        iter->wrap_count = 0;

        /*
         * start with the block with oldest data; if data has wrapped
         * in this window, it should be in this block
         */
        if (msc_block_wrapped(msc_iter_bdesc(iter)))
                iter->wrap_count = 2;

}

static int msc_iter_win_start(struct msc_iter *iter, struct msc *msc)
{
        /* already started, nothing to do */
        if (iter->start_win)
                return 0;

        iter->start_win = msc_oldest_window(msc);
        if (!iter->start_win)
                return -EINVAL;

        iter->win = iter->start_win;
        iter->start_block = -1;

        msc_iter_block_start(iter);

        return 0;
}

static int msc_iter_win_advance(struct msc_iter *iter)
{
        iter->win = msc_next_window(iter->win);
        iter->start_block = -1;

        if (iter->win == iter->start_win) {
                iter->eof++;
                return 1;
        }

        msc_iter_block_start(iter);

        return 0;
}

static int msc_iter_block_advance(struct msc_iter *iter)
{
        iter->block_off = 0;

        /* wrapping */
        if (iter->wrap_count && iter->block == iter->start_block) {
                iter->wrap_count--;
                if (!iter->wrap_count)
                        /* copied newest data from the wrapped block */
                        return msc_iter_win_advance(iter);
        }

        /* no wrapping, check for last written block */
        if (!iter->wrap_count && msc_block_last_written(msc_iter_bdesc(iter)))
                /* copied newest data for the window */
                return msc_iter_win_advance(iter);

        /* block advance */
        if (++iter->block == iter->win->nr_blocks)
                iter->block = 0;

        /* no wrapping, sanity check in case there is no last written block */
        if (!iter->wrap_count && iter->block == iter->start_block)
                return msc_iter_win_advance(iter);

        return 0;
}

/**
 * msc_buffer_iterate() - go through multiblock buffer's data
 * @iter:       iterator structure
 * @size:       amount of data to scan
 * @data:       callback's private data
 * @fn:         iterator callback
 *
 * This will start at the window which will be written to next (containing
 * the oldest data) and work its way to the current window, calling @fn
 * for each chunk of data as it goes.
 *
 * Caller should have msc::user_count reference to make sure the buffer
 * doesn't disappear from under us.
 *
 * Return:      amount of data actually scanned.
 */
static ssize_t
msc_buffer_iterate(struct msc_iter *iter, size_t size, void *data,
                   unsigned long (*fn)(void *, void *, size_t))
{
        struct msc *msc = iter->msc;
        size_t len = size;
        unsigned int advance;

        if (iter->eof)
                return 0;

        /* start with the oldest window */
        if (msc_iter_win_start(iter, msc))
                return 0;

        do {
                unsigned long data_bytes = msc_data_sz(msc_iter_bdesc(iter));
                void *src = (void *)msc_iter_bdesc(iter) + MSC_BDESC;
                size_t tocopy = data_bytes, copied = 0;
                size_t remaining = 0;

                advance = 1;

                /*
                 * If block wrapping happened, we need to visit the last block
                 * twice, because it contains both the oldest and the newest
                 * data in this window.
                 *
                 * First time (wrap_count==2), in the very beginning, to collect
                 * the oldest data, which is in the range
                 * (data_bytes..DATA_IN_PAGE).
                 *
                 * Second time (wrap_count==1), it's just like any other block,
                 * containing data in the range of [MSC_BDESC..data_bytes].
                 */
                if (iter->block == iter->start_block && iter->wrap_count == 2) {
                        tocopy = DATA_IN_PAGE - data_bytes;
                        src += data_bytes;
                }

                if (!tocopy)
                        goto next_block;

                tocopy -= iter->block_off;
                src += iter->block_off;

                if (len < tocopy) {
                        tocopy = len;
                        advance = 0;
                }

                remaining = fn(data, src, tocopy);

                if (remaining)
                        advance = 0;

                copied = tocopy - remaining;
                len -= copied;
                iter->block_off += copied;
                iter->offset += copied;

                if (!advance)
                        break;

next_block:
                if (msc_iter_block_advance(iter))
                        break;

        } while (len);

        return size - len;
}

/**
 * msc_buffer_clear_hw_header() - clear hw header for multiblock
 * @msc:        MSC device
 */
static void msc_buffer_clear_hw_header(struct msc *msc)
{
        struct msc_window *win;

        list_for_each_entry(win, &msc->win_list, entry) {
                unsigned int blk;
                size_t hw_sz = sizeof(struct msc_block_desc) -
                        offsetof(struct msc_block_desc, hw_tag);

                for (blk = 0; blk < win->nr_blocks; blk++) {
                        struct msc_block_desc *bdesc = win->block[blk].bdesc;

                        memset(&bdesc->hw_tag, 0, hw_sz);
                }
        }
}

/**
 * msc_configure() - set up MSC hardware
 * @msc:        the MSC device to configure
 *
 * Program storage mode, wrapping, burst length and trace buffer address
 * into a given MSC. Then, enable tracing and set msc::enabled.
 * The latter is serialized on msc::buf_mutex, so make sure to hold it.
 */
static int msc_configure(struct msc *msc)
{
        u32 reg;

        lockdep_assert_held(&msc->buf_mutex);

        if (msc->mode > MSC_MODE_MULTI)
                return -ENOTSUPP;

        if (msc->mode == MSC_MODE_MULTI)
                msc_buffer_clear_hw_header(msc);

        reg = msc->base_addr >> PAGE_SHIFT;
        iowrite32(reg, msc->reg_base + REG_MSU_MSC0BAR);

        if (msc->mode == MSC_MODE_SINGLE) {
                reg = msc->nr_pages;
                iowrite32(reg, msc->reg_base + REG_MSU_MSC0SIZE);
        }

        reg = ioread32(msc->reg_base + REG_MSU_MSC0CTL);
        reg &= ~(MSC_MODE | MSC_WRAPEN | MSC_EN | MSC_RD_HDR_OVRD);

        reg |= MSC_EN;
        reg |= msc->mode << __ffs(MSC_MODE);
        reg |= msc->burst_len << __ffs(MSC_LEN);

        if (msc->wrap)
                reg |= MSC_WRAPEN;

        iowrite32(reg, msc->reg_base + REG_MSU_MSC0CTL);

        msc->thdev->output.multiblock = msc->mode == MSC_MODE_MULTI;
        intel_th_trace_enable(msc->thdev);
        msc->enabled = 1;


        return 0;
}

/**
 * msc_disable() - disable MSC hardware
 * @msc:        MSC device to disable
 *
 * If @msc is enabled, disable tracing on the switch and then disable MSC
 * storage. Caller must hold msc::buf_mutex.
 */
static void msc_disable(struct msc *msc)
{
        unsigned long count;
        u32 reg;

        lockdep_assert_held(&msc->buf_mutex);

        intel_th_trace_disable(msc->thdev);

        for (reg = 0, count = MSC_PLE_WAITLOOP_DEPTH;
             count && !(reg & MSCSTS_PLE); count--) {
                reg = ioread32(msc->reg_base + REG_MSU_MSC0STS);
                cpu_relax();
        }

        if (!count)
                dev_dbg(msc_dev(msc), "timeout waiting for MSC0 PLE\n");

        if (msc->mode == MSC_MODE_SINGLE) {
                msc->single_wrap = !!(reg & MSCSTS_WRAPSTAT);

                reg = ioread32(msc->reg_base + REG_MSU_MSC0MWP);
                msc->single_sz = reg & ((msc->nr_pages << PAGE_SHIFT) - 1);
                dev_dbg(msc_dev(msc), "MSCnMWP: %08x/%08lx, wrap: %d\n",
                        reg, msc->single_sz, msc->single_wrap);
        }

        reg = ioread32(msc->reg_base + REG_MSU_MSC0CTL);
        reg &= ~MSC_EN;
        iowrite32(reg, msc->reg_base + REG_MSU_MSC0CTL);
        msc->enabled = 0;

        iowrite32(0, msc->reg_base + REG_MSU_MSC0BAR);
        iowrite32(0, msc->reg_base + REG_MSU_MSC0SIZE);

        dev_dbg(msc_dev(msc), "MSCnNWSA: %08x\n",
                ioread32(msc->reg_base + REG_MSU_MSC0NWSA));

        reg = ioread32(msc->reg_base + REG_MSU_MSC0STS);
        dev_dbg(msc_dev(msc), "MSCnSTS: %08x\n", reg);
}

static int intel_th_msc_activate(struct intel_th_device *thdev)
{
        struct msc *msc = dev_get_drvdata(&thdev->dev);
        int ret = -EBUSY;

        if (!atomic_inc_unless_negative(&msc->user_count))
                return -ENODEV;

        mutex_lock(&msc->buf_mutex);

        /* if there are readers, refuse */
        if (list_empty(&msc->iter_list))
                ret = msc_configure(msc);

        mutex_unlock(&msc->buf_mutex);

        if (ret)
                atomic_dec(&msc->user_count);

        return ret;
}

static void intel_th_msc_deactivate(struct intel_th_device *thdev)
{
        struct msc *msc = dev_get_drvdata(&thdev->dev);

        mutex_lock(&msc->buf_mutex);
        if (msc->enabled) {
                msc_disable(msc);
                atomic_dec(&msc->user_count);
        }
        mutex_unlock(&msc->buf_mutex);
}

/**
 * msc_buffer_contig_alloc() - allocate a contiguous buffer for SINGLE mode
 * @msc:        MSC device
 * @size:       allocation size in bytes
 *
 * This modifies msc::base, which requires msc::buf_mutex to serialize, so the
 * caller is expected to hold it.
 *
 * Return:      0 on success, -errno otherwise.
 */
static int msc_buffer_contig_alloc(struct msc *msc, unsigned long size)
{
        unsigned int order = get_order(size);
        struct page *page;

        if (!size)
                return 0;

        page = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
        if (!page)
                return -ENOMEM;

        split_page(page, order);
        msc->nr_pages = size >> PAGE_SHIFT;
        msc->base = page_address(page);
        msc->base_addr = page_to_phys(page);

        return 0;
}

/**
 * msc_buffer_contig_free() - free a contiguous buffer
 * @msc:        MSC configured in SINGLE mode
 */
static void msc_buffer_contig_free(struct msc *msc)
{
        unsigned long off;

        for (off = 0; off < msc->nr_pages << PAGE_SHIFT; off += PAGE_SIZE) {
                struct page *page = virt_to_page(msc->base + off);

                page->mapping = NULL;
                __free_page(page);
        }

        msc->nr_pages = 0;
}

/**
 * msc_buffer_contig_get_page() - find a page at a given offset
 * @msc:        MSC configured in SINGLE mode
 * @pgoff:      page offset
 *
 * Return:      page, if @pgoff is within the range, NULL otherwise.
 */
static struct page *msc_buffer_contig_get_page(struct msc *msc,
                                               unsigned long pgoff)
{
        if (pgoff >= msc->nr_pages)
                return NULL;

        return virt_to_page(msc->base + (pgoff << PAGE_SHIFT));
}

/**
 * msc_buffer_win_alloc() - alloc a window for a multiblock mode
 * @msc:        MSC device
 * @nr_blocks:  number of pages in this window
 *
 * This modifies msc::win_list and msc::base, which requires msc::buf_mutex
 * to serialize, so the caller is expected to hold it.
 *
 * Return:      0 on success, -errno otherwise.
 */
static int msc_buffer_win_alloc(struct msc *msc, unsigned int nr_blocks)
{
        struct msc_window *win;
        unsigned long size = PAGE_SIZE;
        int i, ret = -ENOMEM;

        if (!nr_blocks)
                return 0;

        win = kzalloc(offsetof(struct msc_window, block[nr_blocks]),
                      GFP_KERNEL);
        if (!win)
                return -ENOMEM;

        if (!list_empty(&msc->win_list)) {
                struct msc_window *prev = list_entry(msc->win_list.prev,
                                                     struct msc_window, entry);

                win->pgoff = prev->pgoff + prev->nr_blocks;
        }

        for (i = 0; i < nr_blocks; i++) {
                win->block[i].bdesc = dma_alloc_coherent(msc_dev(msc), size,
                                                         &win->block[i].addr,
                                                         GFP_KERNEL);

#ifdef CONFIG_X86
                /* Set the page as uncached */
                set_memory_uc((unsigned long)win->block[i].bdesc, 1);
#endif

                if (!win->block[i].bdesc)
                        goto err_nomem;
        }

        win->msc = msc;
        win->nr_blocks = nr_blocks;

        if (list_empty(&msc->win_list)) {
                msc->base = win->block[0].bdesc;
                msc->base_addr = win->block[0].addr;
        }

        list_add_tail(&win->entry, &msc->win_list);
        msc->nr_pages += nr_blocks;

        return 0;

err_nomem:
        for (i--; i >= 0; i--) {
#ifdef CONFIG_X86
                /* Reset the page to write-back before releasing */
                set_memory_wb((unsigned long)win->block[i].bdesc, 1);
#endif
                dma_free_coherent(msc_dev(msc), size, win->block[i].bdesc,
                                  win->block[i].addr);
        }
        kfree(win);

        return ret;
}

/**
 * msc_buffer_win_free() - free a window from MSC's window list
 * @msc:        MSC device
 * @win:        window to free
 *
 * This modifies msc::win_list and msc::base, which requires msc::buf_mutex
 * to serialize, so the caller is expected to hold it.
 */
static void msc_buffer_win_free(struct msc *msc, struct msc_window *win)
{
        int i;

        msc->nr_pages -= win->nr_blocks;

        list_del(&win->entry);
        if (list_empty(&msc->win_list)) {
                msc->base = NULL;
                msc->base_addr = 0;
        }

        for (i = 0; i < win->nr_blocks; i++) {
                struct page *page = virt_to_page(win->block[i].bdesc);

                page->mapping = NULL;
#ifdef CONFIG_X86
                /* Reset the page to write-back before releasing */
                set_memory_wb((unsigned long)win->block[i].bdesc, 1);
#endif
                dma_free_coherent(msc_dev(win->msc), PAGE_SIZE,
                                  win->block[i].bdesc, win->block[i].addr);
        }

        kfree(win);
}

/**
 * msc_buffer_relink() - set up block descriptors for multiblock mode
 * @msc:        MSC device
 *
 * This traverses msc::win_list, which requires msc::buf_mutex to serialize,
 * so the caller is expected to hold it.
 */
static void msc_buffer_relink(struct msc *msc)
{
        struct msc_window *win, *next_win;

        /* call with msc::mutex locked */
        list_for_each_entry(win, &msc->win_list, entry) {
                unsigned int blk;
                u32 sw_tag = 0;

                /*
                 * Last window's next_win should point to the first window
                 * and MSC_SW_TAG_LASTWIN should be set.
                 */
                if (msc_is_last_win(win)) {
                        sw_tag |= MSC_SW_TAG_LASTWIN;
                        next_win = list_entry(msc->win_list.next,
                                              struct msc_window, entry);
                } else {
                        next_win = list_entry(win->entry.next,
                                              struct msc_window, entry);
                }

                for (blk = 0; blk < win->nr_blocks; blk++) {
                        struct msc_block_desc *bdesc = win->block[blk].bdesc;

                        memset(bdesc, 0, sizeof(*bdesc));

                        bdesc->next_win = next_win->block[0].addr >> PAGE_SHIFT;

                        /*
                         * Similarly to last window, last block should point
                         * to the first one.
                         */
                        if (blk == win->nr_blocks - 1) {
                                sw_tag |= MSC_SW_TAG_LASTBLK;
                                bdesc->next_blk =
                                        win->block[0].addr >> PAGE_SHIFT;
                        } else {
                                bdesc->next_blk =
                                        win->block[blk + 1].addr >> PAGE_SHIFT;
                        }

                        bdesc->sw_tag = sw_tag;
                        bdesc->block_sz = PAGE_SIZE / 64;
                }
        }

        /*
         * Make the above writes globally visible before tracing is
         * enabled to make sure hardware sees them coherently.
         */
        wmb();
}

static void msc_buffer_multi_free(struct msc *msc)
{
        struct msc_window *win, *iter;

        list_for_each_entry_safe(win, iter, &msc->win_list, entry)
                msc_buffer_win_free(msc, win);
}

static int msc_buffer_multi_alloc(struct msc *msc, unsigned long *nr_pages,
                                  unsigned int nr_wins)
{
        int ret, i;

        for (i = 0; i < nr_wins; i++) {
                ret = msc_buffer_win_alloc(msc, nr_pages[i]);
                if (ret) {
                        msc_buffer_multi_free(msc);
                        return ret;
                }
        }

        msc_buffer_relink(msc);

        return 0;
}

/**
 * msc_buffer_free() - free buffers for MSC
 * @msc:        MSC device
 *
 * Free MSC's storage buffers.
 *
 * This modifies msc::win_list and msc::base, which requires msc::buf_mutex to
 * serialize, so the caller is expected to hold it.
 */
static void msc_buffer_free(struct msc *msc)
{
        if (msc->mode == MSC_MODE_SINGLE)
                msc_buffer_contig_free(msc);
        else if (msc->mode == MSC_MODE_MULTI)
                msc_buffer_multi_free(msc);
}

/**
 * msc_buffer_alloc() - allocate a buffer for MSC
 * @msc:        MSC device
 * @size:       allocation size in bytes
 *
 * Allocate a storage buffer for MSC, depending on the msc::mode, it will be
 * either done via msc_buffer_contig_alloc() for SINGLE operation mode or
 * msc_buffer_win_alloc() for multiblock operation. The latter allocates one
 * window per invocation, so in multiblock mode this can be called multiple
 * times for the same MSC to allocate multiple windows.
 *
 * This modifies msc::win_list and msc::base, which requires msc::buf_mutex
 * to serialize, so the caller is expected to hold it.
 *
 * Return:      0 on success, -errno otherwise.
 */
static int msc_buffer_alloc(struct msc *msc, unsigned long *nr_pages,
                            unsigned int nr_wins)
{
        int ret;

        /* -1: buffer not allocated */
        if (atomic_read(&msc->user_count) != -1)
                return -EBUSY;

        if (msc->mode == MSC_MODE_SINGLE) {
                if (nr_wins != 1)
                        return -EINVAL;

                ret = msc_buffer_contig_alloc(msc, nr_pages[0] << PAGE_SHIFT);
        } else if (msc->mode == MSC_MODE_MULTI) {
                ret = msc_buffer_multi_alloc(msc, nr_pages, nr_wins);
        } else {
                ret = -ENOTSUPP;
        }

        if (!ret) {
                /* allocation should be visible before the counter goes to 0 */
                smp_mb__before_atomic();

                if (WARN_ON_ONCE(atomic_cmpxchg(&msc->user_count, -1, 0) != -1))
                        return -EINVAL;
        }

        return ret;
}

/**
 * msc_buffer_unlocked_free_unless_used() - free a buffer unless it's in use
 * @msc:        MSC device
 *
 * This will free MSC buffer unless it is in use or there is no allocated
 * buffer.
 * Caller needs to hold msc::buf_mutex.
 *
 * Return:      0 on successful deallocation or if there was no buffer to
 *              deallocate, -EBUSY if there are active users.
 */
static int msc_buffer_unlocked_free_unless_used(struct msc *msc)
{
        int count, ret = 0;

        count = atomic_cmpxchg(&msc->user_count, 0, -1);

        /* > 0: buffer is allocated and has users */
        if (count > 0)
                ret = -EBUSY;
        /* 0: buffer is allocated, no users */
        else if (!count)
                msc_buffer_free(msc);
        /* < 0: no buffer, nothing to do */

        return ret;
}

/**
 * msc_buffer_free_unless_used() - free a buffer unless it's in use
 * @msc:        MSC device
 *
 * This is a locked version of msc_buffer_unlocked_free_unless_used().
 */
static int msc_buffer_free_unless_used(struct msc *msc)
{
        int ret;

        mutex_lock(&msc->buf_mutex);
        ret = msc_buffer_unlocked_free_unless_used(msc);
        mutex_unlock(&msc->buf_mutex);

        return ret;
}

/**
 * msc_buffer_get_page() - get MSC buffer page at a given offset
 * @msc:        MSC device
 * @pgoff:      page offset into the storage buffer
 *
 * This traverses msc::win_list, so holding msc::buf_mutex is expected from
 * the caller.
 *
 * Return:      page if @pgoff corresponds to a valid buffer page or NULL.
 */
static struct page *msc_buffer_get_page(struct msc *msc, unsigned long pgoff)
{
        struct msc_window *win;

        if (msc->mode == MSC_MODE_SINGLE)
                return msc_buffer_contig_get_page(msc, pgoff);

        list_for_each_entry(win, &msc->win_list, entry)
                if (pgoff >= win->pgoff && pgoff < win->pgoff + win->nr_blocks)
                        goto found;

        return NULL;

found:
        pgoff -= win->pgoff;
        return virt_to_page(win->block[pgoff].bdesc);
}

/**
 * struct msc_win_to_user_struct - data for copy_to_user() callback
 * @buf:        userspace buffer to copy data to
 * @offset:     running offset
 */
struct msc_win_to_user_struct {
        char __user     *buf;
        unsigned long   offset;
};

/**
 * msc_win_to_user() - iterator for msc_buffer_iterate() to copy data to user
 * @data:       callback's private data
 * @src:        source buffer
 * @len:        amount of data to copy from the source buffer
 */
static unsigned long msc_win_to_user(void *data, void *src, size_t len)
{
        struct msc_win_to_user_struct *u = data;
        unsigned long ret;

        ret = copy_to_user(u->buf + u->offset, src, len);
        u->offset += len - ret;

        return ret;
}


/*
 * file operations' callbacks
 */

static int intel_th_msc_open(struct inode *inode, struct file *file)
{
        struct intel_th_device *thdev = file->private_data;
        struct msc *msc = dev_get_drvdata(&thdev->dev);
        struct msc_iter *iter;

        if (!capable(CAP_SYS_RAWIO))
                return -EPERM;

        iter = msc_iter_install(msc);
        if (IS_ERR(iter))
                return PTR_ERR(iter);

        file->private_data = iter;

        return nonseekable_open(inode, file);
}

static int intel_th_msc_release(struct inode *inode, struct file *file)
{
        struct msc_iter *iter = file->private_data;
        struct msc *msc = iter->msc;

        msc_iter_remove(iter, msc);

        return 0;
}

static ssize_t
msc_single_to_user(struct msc *msc, char __user *buf, loff_t off, size_t len)
{
        unsigned long size = msc->nr_pages << PAGE_SHIFT, rem = len;
        unsigned long start = off, tocopy = 0;

        if (msc->single_wrap) {
                start += msc->single_sz;
                if (start < size) {
                        tocopy = min(rem, size - start);
                        if (copy_to_user(buf, msc->base + start, tocopy))
                                return -EFAULT;

                        buf += tocopy;
                        rem -= tocopy;
                        start += tocopy;
                }

                start &= size - 1;
                if (rem) {
                        tocopy = min(rem, msc->single_sz - start);
                        if (copy_to_user(buf, msc->base + start, tocopy))
                                return -EFAULT;

                        rem -= tocopy;
                }

                return len - rem;
        }

        if (copy_to_user(buf, msc->base + start, rem))
                return -EFAULT;

        return len;
}

static ssize_t intel_th_msc_read(struct file *file, char __user *buf,
                                 size_t len, loff_t *ppos)
{
        struct msc_iter *iter = file->private_data;
        struct msc *msc = iter->msc;
        size_t size;
        loff_t off = *ppos;
        ssize_t ret = 0;

        if (!atomic_inc_unless_negative(&msc->user_count))
                return 0;

        if (msc->mode == MSC_MODE_SINGLE && !msc->single_wrap)
                size = msc->single_sz;
        else
                size = msc->nr_pages << PAGE_SHIFT;

        if (!size)
                goto put_count;

        if (off >= size)
                goto put_count;

        if (off + len >= size)
                len = size - off;

        if (msc->mode == MSC_MODE_SINGLE) {
                ret = msc_single_to_user(msc, buf, off, len);
                if (ret >= 0)
                        *ppos += ret;
        } else if (msc->mode == MSC_MODE_MULTI) {
                struct msc_win_to_user_struct u = {
                        .buf    = buf,
                        .offset = 0,
                };

                ret = msc_buffer_iterate(iter, len, &u, msc_win_to_user);
                if (ret >= 0)
                        *ppos = iter->offset;
        } else {
                ret = -ENOTSUPP;
        }

put_count:
        atomic_dec(&msc->user_count);

        return ret;
}

/*
 * vm operations callbacks (vm_ops)
 */

static void msc_mmap_open(struct vm_area_struct *vma)
{
        struct msc_iter *iter = vma->vm_file->private_data;
        struct msc *msc = iter->msc;

        atomic_inc(&msc->mmap_count);
}

static void msc_mmap_close(struct vm_area_struct *vma)
{
        struct msc_iter *iter = vma->vm_file->private_data;
        struct msc *msc = iter->msc;
        unsigned long pg;

        if (!atomic_dec_and_mutex_lock(&msc->mmap_count, &msc->buf_mutex))
                return;

        /* drop page _refcounts */
        for (pg = 0; pg < msc->nr_pages; pg++) {
                struct page *page = msc_buffer_get_page(msc, pg);

                if (WARN_ON_ONCE(!page))
                        continue;

                if (page->mapping)
                        page->mapping = NULL;
        }

        /* last mapping -- drop user_count */
        atomic_dec(&msc->user_count);
        mutex_unlock(&msc->buf_mutex);
}

static int msc_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct msc_iter *iter = vma->vm_file->private_data;
        struct msc *msc = iter->msc;

        vmf->page = msc_buffer_get_page(msc, vmf->pgoff);
        if (!vmf->page)
                return VM_FAULT_SIGBUS;

        get_page(vmf->page);
        vmf->page->mapping = vma->vm_file->f_mapping;
        vmf->page->index = vmf->pgoff;

        return 0;
}

static const struct vm_operations_struct msc_mmap_ops = {
        .open   = msc_mmap_open,
        .close  = msc_mmap_close,
        .fault  = msc_mmap_fault,
};

static int intel_th_msc_mmap(struct file *file, struct vm_area_struct *vma)
{
        unsigned long size = vma->vm_end - vma->vm_start;
        struct msc_iter *iter = vma->vm_file->private_data;
        struct msc *msc = iter->msc;
        int ret = -EINVAL;

        if (!size || offset_in_page(size))
                return -EINVAL;

        if (vma->vm_pgoff)
                return -EINVAL;

        /* grab user_count once per mmap; drop in msc_mmap_close() */
        if (!atomic_inc_unless_negative(&msc->user_count))
                return -EINVAL;

        if (msc->mode != MSC_MODE_SINGLE &&
            msc->mode != MSC_MODE_MULTI)
                goto out;

        if (size >> PAGE_SHIFT != msc->nr_pages)
                goto out;

        atomic_set(&msc->mmap_count, 1);
        ret = 0;

out:
        if (ret)
                atomic_dec(&msc->user_count);

        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
        vma->vm_flags |= VM_DONTEXPAND | VM_DONTCOPY;
        vma->vm_ops = &msc_mmap_ops;
        return ret;
}

static const struct file_operations intel_th_msc_fops = {
        .open           = intel_th_msc_open,
        .release        = intel_th_msc_release,
        .read           = intel_th_msc_read,
        .mmap           = intel_th_msc_mmap,
        .llseek         = no_llseek,
        .owner          = THIS_MODULE,
};

static int intel_th_msc_init(struct msc *msc)
{
        atomic_set(&msc->user_count, -1);

        msc->mode = MSC_MODE_MULTI;
        mutex_init(&msc->buf_mutex);
        INIT_LIST_HEAD(&msc->win_list);
        INIT_LIST_HEAD(&msc->iter_list);

        msc->burst_len =
                (ioread32(msc->reg_base + REG_MSU_MSC0CTL) & MSC_LEN) >>
                __ffs(MSC_LEN);

        return 0;
}

static const char * const msc_mode[] = {
        [MSC_MODE_SINGLE]       = "single",
        [MSC_MODE_MULTI]        = "multi",
        [MSC_MODE_EXI]          = "ExI",
        [MSC_MODE_DEBUG]        = "debug",
};

static ssize_t
wrap_show(struct device *dev, struct device_attribute *attr, char *buf)
{
        struct msc *msc = dev_get_drvdata(dev);

        return scnprintf(buf, PAGE_SIZE, "%d\n", msc->wrap);
}

static ssize_t
wrap_store(struct device *dev, struct device_attribute *attr, const char *buf,
           size_t size)
{
        struct msc *msc = dev_get_drvdata(dev);
        unsigned long val;
        int ret;

        ret = kstrtoul(buf, 10, &val);
        if (ret)
                return ret;

        msc->wrap = !!val;

        return size;
}

static DEVICE_ATTR_RW(wrap);

static ssize_t
mode_show(struct device *dev, struct device_attribute *attr, char *buf)
{
        struct msc *msc = dev_get_drvdata(dev);

        return scnprintf(buf, PAGE_SIZE, "%s\n", msc_mode[msc->mode]);
}

static ssize_t
mode_store(struct device *dev, struct device_attribute *attr, const char *buf,
           size_t size)
{
        struct msc *msc = dev_get_drvdata(dev);
        size_t len = size;
        char *cp;
        int i, ret;

        if (!capable(CAP_SYS_RAWIO))
                return -EPERM;

        cp = memchr(buf, '\n', len);
        if (cp)
                len = cp - buf;

        for (i = 0; i < ARRAY_SIZE(msc_mode); i++)
                if (!strncmp(msc_mode[i], buf, len))
                        goto found;

        return -EINVAL;

found:
        mutex_lock(&msc->buf_mutex);
        ret = msc_buffer_unlocked_free_unless_used(msc);
        if (!ret)
                msc->mode = i;
        mutex_unlock(&msc->buf_mutex);

        return ret ? ret : size;
}

static DEVICE_ATTR_RW(mode);

static ssize_t
nr_pages_show(struct device *dev, struct device_attribute *attr, char *buf)
{
        struct msc *msc = dev_get_drvdata(dev);
        struct msc_window *win;
        size_t count = 0;

        mutex_lock(&msc->buf_mutex);

        if (msc->mode == MSC_MODE_SINGLE)
                count = scnprintf(buf, PAGE_SIZE, "%ld\n", msc->nr_pages);
        else if (msc->mode == MSC_MODE_MULTI) {
                list_for_each_entry(win, &msc->win_list, entry) {
                        count += scnprintf(buf + count, PAGE_SIZE - count,
                                           "%d%c", win->nr_blocks,
                                           msc_is_last_win(win) ? '\n' : ',');
                }
        } else {
                count = scnprintf(buf, PAGE_SIZE, "unsupported\n");
        }

        mutex_unlock(&msc->buf_mutex);

        return count;
}

static ssize_t
nr_pages_store(struct device *dev, struct device_attribute *attr,
               const char *buf, size_t size)
{
        struct msc *msc = dev_get_drvdata(dev);
        unsigned long val, *win = NULL, *rewin;
        size_t len = size;
        const char *p = buf;
        char *end, *s;
        int ret, nr_wins = 0;

        if (!capable(CAP_SYS_RAWIO))
                return -EPERM;

        ret = msc_buffer_free_unless_used(msc);
        if (ret)
                return ret;

        /* scan the comma-separated list of allocation sizes */
        end = memchr(buf, '\n', len);
        if (end)
                len = end - buf;

        do {
                end = memchr(p, ',', len);
                s = kstrndup(p, end ? end - p : len, GFP_KERNEL);
                if (!s) {
                        ret = -ENOMEM;
                        goto free_win;
                }

                ret = kstrtoul(s, 10, &val);
                kfree(s);

                if (ret || !val)
                        goto free_win;

                if (nr_wins && msc->mode == MSC_MODE_SINGLE) {
                        ret = -EINVAL;
                        goto free_win;
                }

                nr_wins++;
                rewin = krealloc(win, sizeof(*win) * nr_wins, GFP_KERNEL);
                if (!rewin) {
                        kfree(win);
                        return -ENOMEM;
                }

                win = rewin;
                win[nr_wins - 1] = val;

                if (!end)
                        break;

                len -= end - p;
                p = end + 1;
        } while (len);

        mutex_lock(&msc->buf_mutex);
        ret = msc_buffer_alloc(msc, win, nr_wins);
        mutex_unlock(&msc->buf_mutex);

free_win:
        kfree(win);

        return ret ? ret : size;
}

static DEVICE_ATTR_RW(nr_pages);

static struct attribute *msc_output_attrs[] = {
        &dev_attr_wrap.attr,
        &dev_attr_mode.attr,
        &dev_attr_nr_pages.attr,
        NULL,
};

static struct attribute_group msc_output_group = {
        .attrs  = msc_output_attrs,
};

static int intel_th_msc_probe(struct intel_th_device *thdev)
{
        struct device *dev = &thdev->dev;
        struct resource *res;
        struct msc *msc;
        void __iomem *base;
        int err;

        res = intel_th_device_get_resource(thdev, IORESOURCE_MEM, 0);
        if (!res)
                return -ENODEV;

        base = devm_ioremap(dev, res->start, resource_size(res));
        if (!base)
                return -ENOMEM;

        msc = devm_kzalloc(dev, sizeof(*msc), GFP_KERNEL);
        if (!msc)
                return -ENOMEM;

        msc->index = thdev->id;

        msc->thdev = thdev;
        msc->reg_base = base + msc->index * 0x100;

        err = intel_th_msc_init(msc);
        if (err)
                return err;

        dev_set_drvdata(dev, msc);

        return 0;
}

static void intel_th_msc_remove(struct intel_th_device *thdev)
{
        struct msc *msc = dev_get_drvdata(&thdev->dev);
        int ret;

        intel_th_msc_deactivate(thdev);

        /*
         * Buffers should not be used at this point except if the
         * output character device is still open and the parent
         * device gets detached from its bus, which is a FIXME.
         */
        ret = msc_buffer_free_unless_used(msc);
        WARN_ON_ONCE(ret);
}

static struct intel_th_driver intel_th_msc_driver = {
        .probe  = intel_th_msc_probe,
        .remove = intel_th_msc_remove,
        .activate       = intel_th_msc_activate,
        .deactivate     = intel_th_msc_deactivate,
        .fops   = &intel_th_msc_fops,
        .attr_group     = &msc_output_group,
        .driver = {
                .name   = "msc",
                .owner  = THIS_MODULE,
        },
};

module_driver(intel_th_msc_driver,
              intel_th_driver_register,
              intel_th_driver_unregister);

MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Intel(R) Trace Hub Memory Storage Unit driver");
MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");