/**
 * imr.c -- Intel Isolated Memory Region driver
 *
 * Copyright(c) 2013 Intel Corporation.
 * Copyright(c) 2015 Bryan O'Donoghue <pure.logic@nexus-software.ie>
 *
 * IMR registers define an isolated region of memory that can
 * be masked to prohibit certain system agents from accessing memory.
 * When a device behind a masked port performs an access - snooped or
 * not, an IMR may optionally prevent that transaction from changing
 * the state of memory or from getting correct data in response to the
 * operation.
 *
 * Write data will be dropped and reads will return 0xFFFFFFFF, the
 * system will reset and system BIOS will print out an error message to
 * inform the user that an IMR has been violated.
 *
 * This code is based on the Linux MTRR code and reference code from
 * Intel's Quark BSP EFI, Linux and grub code.
 *
 * See quark-x1000-datasheet.pdf for register definitions.
 * http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/quark-x1000-datasheet.pdf
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <asm-generic/sections.h>
#include <asm/cpu_device_id.h>
#include <asm/imr.h>
#include <asm/iosf_mbi.h>
#include <linux/debugfs.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/types.h>

struct imr_device {
        struct dentry   *file;
        bool            init;
        struct mutex    lock;
        int             max_imr;
        int             reg_base;
};

static struct imr_device imr_dev;

/*
 * IMR read/write mask control registers.
 * See quark-x1000-datasheet.pdf sections 12.7.4.5 and 12.7.4.6 for
 * bit definitions.
 *
 * addr_hi
 * 31           Lock bit
 * 30:24        Reserved
 * 23:2         1 KiB aligned lo address
 * 1:0          Reserved
 *
 * addr_hi
 * 31:24        Reserved
 * 23:2         1 KiB aligned hi address
 * 1:0          Reserved
 */
#define IMR_LOCK        BIT(31)

struct imr_regs {
        u32 addr_lo;
        u32 addr_hi;
        u32 rmask;
        u32 wmask;
};

#define IMR_NUM_REGS    (sizeof(struct imr_regs)/sizeof(u32))
#define IMR_SHIFT       8
#define imr_to_phys(x)  ((x) << IMR_SHIFT)
#define phys_to_imr(x)  ((x) >> IMR_SHIFT)

/**
 * imr_is_enabled - true if an IMR is enabled false otherwise.
 *
 * Determines if an IMR is enabled based on address range and read/write
 * mask. An IMR set with an address range set to zero and a read/write
 * access mask set to all is considered to be disabled. An IMR in any
 * other state - for example set to zero but without read/write access
 * all is considered to be enabled. This definition of disabled is how
 * firmware switches off an IMR and is maintained in kernel for
 * consistency.
 *
 * @imr:        pointer to IMR descriptor.
 * @return:     true if IMR enabled false if disabled.
 */
static inline int imr_is_enabled(struct imr_regs *imr)
{
        return !(imr->rmask == IMR_READ_ACCESS_ALL &&
                 imr->wmask == IMR_WRITE_ACCESS_ALL &&
                 imr_to_phys(imr->addr_lo) == 0 &&
                 imr_to_phys(imr->addr_hi) == 0);
}

/**
 * imr_read - read an IMR at a given index.
 *
 * Requires caller to hold imr mutex.
 *
 * @idev:       pointer to imr_device structure.
 * @imr_id:     IMR entry to read.
 * @imr:        IMR structure representing address and access masks.
 * @return:     0 on success or error code passed from mbi_iosf on failure.
 */
static int imr_read(struct imr_device *idev, u32 imr_id, struct imr_regs *imr)
{
        u32 reg = imr_id * IMR_NUM_REGS + idev->reg_base;
        int ret;

        ret = iosf_mbi_read(QRK_MBI_UNIT_MM, MBI_REG_READ, reg++, &imr->addr_lo);
        if (ret)
                return ret;

        ret = iosf_mbi_read(QRK_MBI_UNIT_MM, MBI_REG_READ, reg++, &imr->addr_hi);
        if (ret)
                return ret;

        ret = iosf_mbi_read(QRK_MBI_UNIT_MM, MBI_REG_READ, reg++, &imr->rmask);
        if (ret)
                return ret;

        return iosf_mbi_read(QRK_MBI_UNIT_MM, MBI_REG_READ, reg++, &imr->wmask);
}

/**
 * imr_write - write an IMR at a given index.
 *
 * Requires caller to hold imr mutex.
 * Note lock bits need to be written independently of address bits.
 *
 * @idev:       pointer to imr_device structure.
 * @imr_id:     IMR entry to write.
 * @imr:        IMR structure representing address and access masks.
 * @return:     0 on success or error code passed from mbi_iosf on failure.
 */
static int imr_write(struct imr_device *idev, u32 imr_id, struct imr_regs *imr)
{
        unsigned long flags;
        u32 reg = imr_id * IMR_NUM_REGS + idev->reg_base;
        int ret;

        local_irq_save(flags);

        ret = iosf_mbi_write(QRK_MBI_UNIT_MM, MBI_REG_WRITE, reg++, imr->addr_lo);
        if (ret)
                goto failed;

        ret = iosf_mbi_write(QRK_MBI_UNIT_MM, MBI_REG_WRITE, reg++, imr->addr_hi);
        if (ret)
                goto failed;

        ret = iosf_mbi_write(QRK_MBI_UNIT_MM, MBI_REG_WRITE, reg++, imr->rmask);
        if (ret)
                goto failed;

        ret = iosf_mbi_write(QRK_MBI_UNIT_MM, MBI_REG_WRITE, reg++, imr->wmask);
        if (ret)
                goto failed;

        local_irq_restore(flags);
        return 0;
failed:
        /*
         * If writing to the IOSF failed then we're in an unknown state,
         * likely a very bad state. An IMR in an invalid state will almost
         * certainly lead to a memory access violation.
         */
        local_irq_restore(flags);
        WARN(ret, "IOSF-MBI write fail range 0x%08x-0x%08x unreliable\n",
             imr_to_phys(imr->addr_lo), imr_to_phys(imr->addr_hi) + IMR_MASK);

        return ret;
}

/**
 * imr_dbgfs_state_show - print state of IMR registers.
 *
 * @s:          pointer to seq_file for output.
 * @unused:     unused parameter.
 * @return:     0 on success or error code passed from mbi_iosf on failure.
 */
static int imr_dbgfs_state_show(struct seq_file *s, void *unused)
{
        phys_addr_t base;
        phys_addr_t end;
        int i;
        struct imr_device *idev = s->private;
        struct imr_regs imr;
        size_t size;
        int ret = -ENODEV;

        mutex_lock(&idev->lock);

        for (i = 0; i < idev->max_imr; i++) {

                ret = imr_read(idev, i, &imr);
                if (ret)
                        break;

                /*
                 * Remember to add IMR_ALIGN bytes to size to indicate the
                 * inherent IMR_ALIGN size bytes contained in the masked away
                 * lower ten bits.
                 */
                if (imr_is_enabled(&imr)) {
                        base = imr_to_phys(imr.addr_lo);
                        end = imr_to_phys(imr.addr_hi) + IMR_MASK;
                        size = end - base + 1;
                } else {
                        base = 0;
                        end = 0;
                        size = 0;
                }
                seq_printf(s, "imr%02i: base=%pa, end=%pa, size=0x%08zx "
                           "rmask=0x%08x, wmask=0x%08x, %s, %s\n", i,
                           &base, &end, size, imr.rmask, imr.wmask,
                           imr_is_enabled(&imr) ? "enabled " : "disabled",
                           imr.addr_lo & IMR_LOCK ? "locked" : "unlocked");
        }

        mutex_unlock(&idev->lock);
        return ret;
}

/**
 * imr_state_open - debugfs open callback.
 *
 * @inode:      pointer to struct inode.
 * @file:       pointer to struct file.
 * @return:     result of single open.
 */
static int imr_state_open(struct inode *inode, struct file *file)
{
        return single_open(file, imr_dbgfs_state_show, inode->i_private);
}

static const struct file_operations imr_state_ops = {
        .open           = imr_state_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

/**
 * imr_debugfs_register - register debugfs hooks.
 *
 * @idev:       pointer to imr_device structure.
 * @return:     0 on success - errno on failure.
 */
static int imr_debugfs_register(struct imr_device *idev)
{
        idev->file = debugfs_create_file("imr_state", S_IFREG | S_IRUGO, NULL,
                                         idev, &imr_state_ops);
        return PTR_ERR_OR_ZERO(idev->file);
}

/**
 * imr_check_params - check passed address range IMR alignment and non-zero size
 *
 * @base:       base address of intended IMR.
 * @size:       size of intended IMR.
 * @return:     zero on valid range -EINVAL on unaligned base/size.
 */
static int imr_check_params(phys_addr_t base, size_t size)
{
        if ((base & IMR_MASK) || (size & IMR_MASK)) {
                pr_err("base %pa size 0x%08zx must align to 1KiB\n",
                        &base, size);
                return -EINVAL;
        }
        if (size == 0)
                return -EINVAL;

        return 0;
}

/**
 * imr_raw_size - account for the IMR_ALIGN bytes that addr_hi appends.
 *
 * IMR addr_hi has a built in offset of plus IMR_ALIGN (0x400) bytes from the
 * value in the register. We need to subtract IMR_ALIGN bytes from input sizes
 * as a result.
 *
 * @size:       input size bytes.
 * @return:     reduced size.
 */
static inline size_t imr_raw_size(size_t size)
{
        return size - IMR_ALIGN;
}

/**
 * imr_address_overlap - detects an address overlap.
 *
 * @addr:       address to check against an existing IMR.
 * @imr:        imr being checked.
 * @return:     true for overlap false for no overlap.
 */
static inline int imr_address_overlap(phys_addr_t addr, struct imr_regs *imr)
{
        return addr >= imr_to_phys(imr->addr_lo) && addr <= imr_to_phys(imr->addr_hi);
}

/**
 * imr_add_range - add an Isolated Memory Region.
 *
 * @base:       physical base address of region aligned to 1KiB.
 * @size:       physical size of region in bytes must be aligned to 1KiB.
 * @read_mask:  read access mask.
 * @write_mask: write access mask.
 * @return:     zero on success or negative value indicating error.
 */
int imr_add_range(phys_addr_t base, size_t size,
                  unsigned int rmask, unsigned int wmask)
{
        phys_addr_t end;
        unsigned int i;
        struct imr_device *idev = &imr_dev;
        struct imr_regs imr;
        size_t raw_size;
        int reg;
        int ret;

        if (WARN_ONCE(idev->init == false, "driver not initialized"))
                return -ENODEV;

        ret = imr_check_params(base, size);
        if (ret)
                return ret;

        /* Tweak the size value. */
        raw_size = imr_raw_size(size);
        end = base + raw_size;

        /*
         * Check for reserved IMR value common to firmware, kernel and grub
         * indicating a disabled IMR.
         */
        imr.addr_lo = phys_to_imr(base);
        imr.addr_hi = phys_to_imr(end);
        imr.rmask = rmask;
        imr.wmask = wmask;
        if (!imr_is_enabled(&imr))
                return -ENOTSUPP;

        mutex_lock(&idev->lock);

        /*
         * Find a free IMR while checking for an existing overlapping range.
         * Note there's no restriction in silicon to prevent IMR overlaps.
         * For the sake of simplicity and ease in defining/debugging an IMR
         * memory map we exclude IMR overlaps.
         */
        reg = -1;
        for (i = 0; i < idev->max_imr; i++) {
                ret = imr_read(idev, i, &imr);
                if (ret)
                        goto failed;

                /* Find overlap @ base or end of requested range. */
                ret = -EINVAL;
                if (imr_is_enabled(&imr)) {
                        if (imr_address_overlap(base, &imr))
                                goto failed;
                        if (imr_address_overlap(end, &imr))
                                goto failed;
                } else {
                        reg = i;
                }
        }

        /* Error out if we have no free IMR entries. */
        if (reg == -1) {
                ret = -ENOMEM;
                goto failed;
        }

        pr_debug("add %d phys %pa-%pa size %zx mask 0x%08x wmask 0x%08x\n",
                 reg, &base, &end, raw_size, rmask, wmask);

        /* Enable IMR at specified range and access mask. */
        imr.addr_lo = phys_to_imr(base);
        imr.addr_hi = phys_to_imr(end);
        imr.rmask = rmask;
        imr.wmask = wmask;

        ret = imr_write(idev, reg, &imr);
        if (ret < 0) {
                /*
                 * In the highly unlikely event iosf_mbi_write failed
                 * attempt to rollback the IMR setup skipping the trapping
                 * of further IOSF write failures.
                 */
                imr.addr_lo = 0;
                imr.addr_hi = 0;
                imr.rmask = IMR_READ_ACCESS_ALL;
                imr.wmask = IMR_WRITE_ACCESS_ALL;
                imr_write(idev, reg, &imr);
        }
failed:
        mutex_unlock(&idev->lock);
        return ret;
}
EXPORT_SYMBOL_GPL(imr_add_range);

/**
 * __imr_remove_range - delete an Isolated Memory Region.
 *
 * This function allows you to delete an IMR by its index specified by reg or
 * by address range specified by base and size respectively. If you specify an
 * index on its own the base and size parameters are ignored.
 * imr_remove_range(0, base, size); delete IMR at index 0 base/size ignored.
 * imr_remove_range(-1, base, size); delete IMR from base to base+size.
 *
 * @reg:        imr index to remove.
 * @base:       physical base address of region aligned to 1 KiB.
 * @size:       physical size of region in bytes aligned to 1 KiB.
 * @return:     -EINVAL on invalid range or out or range id
 *              -ENODEV if reg is valid but no IMR exists or is locked
 *              0 on success.
 */
static int __imr_remove_range(int reg, phys_addr_t base, size_t size)
{
        phys_addr_t end;
        bool found = false;
        unsigned int i;
        struct imr_device *idev = &imr_dev;
        struct imr_regs imr;
        size_t raw_size;
        int ret = 0;

        if (WARN_ONCE(idev->init == false, "driver not initialized"))
                return -ENODEV;

        /*
         * Validate address range if deleting by address, else we are
         * deleting by index where base and size will be ignored.
         */
        if (reg == -1) {
                ret = imr_check_params(base, size);
                if (ret)
                        return ret;
        }

        /* Tweak the size value. */
        raw_size = imr_raw_size(size);
        end = base + raw_size;

        mutex_lock(&idev->lock);

        if (reg >= 0) {
                /* If a specific IMR is given try to use it. */
                ret = imr_read(idev, reg, &imr);
                if (ret)
                        goto failed;

                if (!imr_is_enabled(&imr) || imr.addr_lo & IMR_LOCK) {
                        ret = -ENODEV;
                        goto failed;
                }
                found = true;
        } else {
                /* Search for match based on address range. */
                for (i = 0; i < idev->max_imr; i++) {
                        ret = imr_read(idev, i, &imr);
                        if (ret)
                                goto failed;

                        if (!imr_is_enabled(&imr) || imr.addr_lo & IMR_LOCK)
                                continue;

                        if ((imr_to_phys(imr.addr_lo) == base) &&
                            (imr_to_phys(imr.addr_hi) == end)) {
                                found = true;
                                reg = i;
                                break;
                        }
                }
        }

        if (!found) {
                ret = -ENODEV;
                goto failed;
        }

        pr_debug("remove %d phys %pa-%pa size %zx\n", reg, &base, &end, raw_size);

        /* Tear down the IMR. */
        imr.addr_lo = 0;
        imr.addr_hi = 0;
        imr.rmask = IMR_READ_ACCESS_ALL;
        imr.wmask = IMR_WRITE_ACCESS_ALL;

        ret = imr_write(idev, reg, &imr);

failed:
        mutex_unlock(&idev->lock);
        return ret;
}

/**
 * imr_remove_range - delete an Isolated Memory Region by address
 *
 * This function allows you to delete an IMR by an address range specified
 * by base and size respectively.
 * imr_remove_range(base, size); delete IMR from base to base+size.
 *
 * @base:       physical base address of region aligned to 1 KiB.
 * @size:       physical size of region in bytes aligned to 1 KiB.
 * @return:     -EINVAL on invalid range or out or range id
 *              -ENODEV if reg is valid but no IMR exists or is locked
 *              0 on success.
 */
int imr_remove_range(phys_addr_t base, size_t size)
{
        return __imr_remove_range(-1, base, size);
}
EXPORT_SYMBOL_GPL(imr_remove_range);

/**
 * imr_clear - delete an Isolated Memory Region by index
 *
 * This function allows you to delete an IMR by an address range specified
 * by the index of the IMR. Useful for initial sanitization of the IMR
 * address map.
 * imr_ge(base, size); delete IMR from base to base+size.
 *
 * @reg:        imr index to remove.
 * @return:     -EINVAL on invalid range or out or range id
 *              -ENODEV if reg is valid but no IMR exists or is locked
 *              0 on success.
 */
static inline int imr_clear(int reg)
{
        return __imr_remove_range(reg, 0, 0);
}

/**
 * imr_fixup_memmap - Tear down IMRs used during bootup.
 *
 * BIOS and Grub both setup IMRs around compressed kernel, initrd memory
 * that need to be removed before the kernel hands out one of the IMR
 * encased addresses to a downstream DMA agent such as the SD or Ethernet.
 * IMRs on Galileo are setup to immediately reset the system on violation.
 * As a result if you're running a root filesystem from SD - you'll need
 * the boot-time IMRs torn down or you'll find seemingly random resets when
 * using your filesystem.
 *
 * @idev:       pointer to imr_device structure.
 * @return:
 */
static void __init imr_fixup_memmap(struct imr_device *idev)
{
        phys_addr_t base = virt_to_phys(&_text);
        size_t size = virt_to_phys(&__end_rodata) - base;
        unsigned long start, end;
        int i;
        int ret;

        /* Tear down all existing unlocked IMRs. */
        for (i = 0; i < idev->max_imr; i++)
                imr_clear(i);

        start = (unsigned long)_text;
        end = (unsigned long)__end_rodata - 1;

        /*
         * Setup an unlocked IMR around the physical extent of the kernel
         * from the beginning of the .text secton to the end of the
         * .rodata section as one physically contiguous block.
         *
         * We don't round up @size since it is already PAGE_SIZE aligned.
         * See vmlinux.lds.S for details.
         */
        ret = imr_add_range(base, size, IMR_CPU, IMR_CPU);
        if (ret < 0) {
                pr_err("unable to setup IMR for kernel: %zu KiB (%lx - %lx)\n",
                        size / 1024, start, end);
        } else {
                pr_info("protecting kernel .text - .rodata: %zu KiB (%lx - %lx)\n",
                        size / 1024, start, end);
        }

}

static const struct x86_cpu_id imr_ids[] __initconst = {
        { X86_VENDOR_INTEL, 5, 9 },     /* Intel Quark SoC X1000. */
        {}
};

/**
 * imr_init - entry point for IMR driver.
 *
 * return: -ENODEV for no IMR support 0 if good to go.
 */
static int __init imr_init(void)
{
        struct imr_device *idev = &imr_dev;
        int ret;

        if (!x86_match_cpu(imr_ids) || !iosf_mbi_available())
                return -ENODEV;

        idev->max_imr = QUARK_X1000_IMR_MAX;
        idev->reg_base = QUARK_X1000_IMR_REGBASE;
        idev->init = true;

        mutex_init(&idev->lock);
        ret = imr_debugfs_register(idev);
        if (ret != 0)
                pr_warn("debugfs register failed!\n");
        imr_fixup_memmap(idev);
        return 0;
}
device_initcall(imr_init);