/*
 *      Copyright (C) 2014 Linaro Ltd.
 *      Author: Ashwin Chaugule <ashwin.chaugule@linaro.org>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that 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.
 *
 *  PCC (Platform Communication Channel) is defined in the ACPI 5.0+
 *  specification. It is a mailbox like mechanism to allow clients
 *  such as CPPC (Collaborative Processor Performance Control), RAS
 *  (Reliability, Availability and Serviceability) and MPST (Memory
 *  Node Power State Table) to talk to the platform (e.g. BMC) through
 *  shared memory regions as defined in the PCC table entries. The PCC
 *  specification supports a Doorbell mechanism for the PCC clients
 *  to notify the platform about new data. This Doorbell information
 *  is also specified in each PCC table entry.
 *
 *  Typical high level flow of operation is:
 *
 *  PCC Reads:
 *  * Client tries to acquire a channel lock.
 *  * After it is acquired it writes READ cmd in communication region cmd
 *              address.
 *  * Client issues mbox_send_message() which rings the PCC doorbell
 *              for its PCC channel.
 *  * If command completes, then client has control over channel and
 *              it can proceed with its reads.
 *  * Client releases lock.
 *
 *  PCC Writes:
 *  * Client tries to acquire channel lock.
 *  * Client writes to its communication region after it acquires a
 *              channel lock.
 *  * Client writes WRITE cmd in communication region cmd address.
 *  * Client issues mbox_send_message() which rings the PCC doorbell
 *              for its PCC channel.
 *  * If command completes, then writes have succeded and it can release
 *              the channel lock.
 *
 *  There is a Nominal latency defined for each channel which indicates
 *  how long to wait until a command completes. If command is not complete
 *  the client needs to retry or assume failure.
 *
 *      For more details about PCC, please see the ACPI specification from
 *  http://www.uefi.org/ACPIv5.1 Section 14.
 *
 *  This file implements PCC as a Mailbox controller and allows for PCC
 *  clients to be implemented as its Mailbox Client Channels.
 */

#include <linux/acpi.h>
#include <linux/delay.h>
#include <linux/io.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/platform_device.h>
#include <linux/mailbox_controller.h>
#include <linux/mailbox_client.h>

#include "mailbox.h"

#define MAX_PCC_SUBSPACES       256

static struct mbox_chan *pcc_mbox_channels;

static struct mbox_controller pcc_mbox_ctrl = {};
/**
 * get_pcc_channel - Given a PCC subspace idx, get
 *      the respective mbox_channel.
 * @id: PCC subspace index.
 *
 * Return: ERR_PTR(errno) if error, else pointer
 *      to mbox channel.
 */
static struct mbox_chan *get_pcc_channel(int id)
{
        struct mbox_chan *pcc_chan;

        if (id < 0 || id > pcc_mbox_ctrl.num_chans)
                return ERR_PTR(-ENOENT);

        pcc_chan = (struct mbox_chan *)
                (unsigned long) pcc_mbox_channels +
                (id * sizeof(*pcc_chan));

        return pcc_chan;
}

/**
 * pcc_mbox_request_channel - PCC clients call this function to
 *              request a pointer to their PCC subspace, from which they
 *              can get the details of communicating with the remote.
 * @cl: Pointer to Mailbox client, so we know where to bind the
 *              Channel.
 * @subspace_id: The PCC Subspace index as parsed in the PCC client
 *              ACPI package. This is used to lookup the array of PCC
 *              subspaces as parsed by the PCC Mailbox controller.
 *
 * Return: Pointer to the Mailbox Channel if successful or
 *              ERR_PTR.
 */
struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
                int subspace_id)
{
        struct device *dev = pcc_mbox_ctrl.dev;
        struct mbox_chan *chan;
        unsigned long flags;

        /*
         * Each PCC Subspace is a Mailbox Channel.
         * The PCC Clients get their PCC Subspace ID
         * from their own tables and pass it here.
         * This returns a pointer to the PCC subspace
         * for the Client to operate on.
         */
        chan = get_pcc_channel(subspace_id);

        if (!chan || chan->cl) {
                dev_err(dev, "Channel not found for idx: %d\n", subspace_id);
                return ERR_PTR(-EBUSY);
        }

        spin_lock_irqsave(&chan->lock, flags);
        chan->msg_free = 0;
        chan->msg_count = 0;
        chan->active_req = NULL;
        chan->cl = cl;
        init_completion(&chan->tx_complete);

        if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
                chan->txdone_method |= TXDONE_BY_ACK;

        spin_unlock_irqrestore(&chan->lock, flags);

        return chan;
}
EXPORT_SYMBOL_GPL(pcc_mbox_request_channel);

/**
 * pcc_mbox_free_channel - Clients call this to free their Channel.
 *
 * @chan: Pointer to the mailbox channel as returned by
 *              pcc_mbox_request_channel()
 */
void pcc_mbox_free_channel(struct mbox_chan *chan)
{
        unsigned long flags;

        if (!chan || !chan->cl)
                return;

        spin_lock_irqsave(&chan->lock, flags);
        chan->cl = NULL;
        chan->active_req = NULL;
        if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
                chan->txdone_method = TXDONE_BY_POLL;

        spin_unlock_irqrestore(&chan->lock, flags);
}
EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);

/**
 * pcc_send_data - Called from Mailbox Controller code. Used
 *              here only to ring the channel doorbell. The PCC client
 *              specific read/write is done in the client driver in
 *              order to maintain atomicity over PCC channel once
 *              OS has control over it. See above for flow of operations.
 * @chan: Pointer to Mailbox channel over which to send data.
 * @data: Client specific data written over channel. Used here
 *              only for debug after PCC transaction completes.
 *
 * Return: Err if something failed else 0 for success.
 */
static int pcc_send_data(struct mbox_chan *chan, void *data)
{
        struct acpi_pcct_hw_reduced *pcct_ss = chan->con_priv;
        struct acpi_generic_address doorbell;
        u64 doorbell_preserve;
        u64 doorbell_val;
        u64 doorbell_write;

        doorbell = pcct_ss->doorbell_register;
        doorbell_preserve = pcct_ss->preserve_mask;
        doorbell_write = pcct_ss->write_mask;

        /* Sync notification from OS to Platform. */
        acpi_read(&doorbell_val, &doorbell);
        acpi_write((doorbell_val & doorbell_preserve) | doorbell_write,
                        &doorbell);

        return 0;
}

static struct mbox_chan_ops pcc_chan_ops = {
        .send_data = pcc_send_data,
};

/**
 * parse_pcc_subspace - Parse the PCC table and verify PCC subspace
 *              entries. There should be one entry per PCC client.
 * @header: Pointer to the ACPI subtable header under the PCCT.
 * @end: End of subtable entry.
 *
 * Return: 0 for Success, else errno.
 *
 * This gets called for each entry in the PCC table.
 */
static int parse_pcc_subspace(struct acpi_subtable_header *header,
                const unsigned long end)
{
        struct acpi_pcct_hw_reduced *pcct_ss;

        if (pcc_mbox_ctrl.num_chans <= MAX_PCC_SUBSPACES) {
                pcct_ss = (struct acpi_pcct_hw_reduced *) header;

                if (pcct_ss->header.type !=
                                ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE) {
                        pr_err("Incorrect PCC Subspace type detected\n");
                        return -EINVAL;
                }
        }

        return 0;
}

/**
 * acpi_pcc_probe - Parse the ACPI tree for the PCCT.
 *
 * Return: 0 for Success, else errno.
 */
static int __init acpi_pcc_probe(void)
{
        acpi_size pcct_tbl_header_size;
        struct acpi_table_header *pcct_tbl;
        struct acpi_subtable_header *pcct_entry;
        int count, i;
        acpi_status status = AE_OK;

        /* Search for PCCT */
        status = acpi_get_table_with_size(ACPI_SIG_PCCT, 0,
                        &pcct_tbl,
                        &pcct_tbl_header_size);

        if (ACPI_FAILURE(status) || !pcct_tbl) {
                pr_warn("PCCT header not found.\n");
                return -ENODEV;
        }

        count = acpi_table_parse_entries(ACPI_SIG_PCCT,
                        sizeof(struct acpi_table_pcct),
                        ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE,
                        parse_pcc_subspace, MAX_PCC_SUBSPACES);

        if (count <= 0) {
                pr_err("Error parsing PCC subspaces from PCCT\n");
                return -EINVAL;
        }

        pcc_mbox_channels = kzalloc(sizeof(struct mbox_chan) *
                        count, GFP_KERNEL);

        if (!pcc_mbox_channels) {
                pr_err("Could not allocate space for PCC mbox channels\n");
                return -ENOMEM;
        }

        /* Point to the first PCC subspace entry */
        pcct_entry = (struct acpi_subtable_header *) (
                (unsigned long) pcct_tbl + sizeof(struct acpi_table_pcct));

        for (i = 0; i < count; i++) {
                pcc_mbox_channels[i].con_priv = pcct_entry;
                pcct_entry = (struct acpi_subtable_header *)
                        ((unsigned long) pcct_entry + pcct_entry->length);
        }

        pcc_mbox_ctrl.num_chans = count;

        pr_info("Detected %d PCC Subspaces\n", pcc_mbox_ctrl.num_chans);

        return 0;
}

/**
 * pcc_mbox_probe - Called when we find a match for the
 *      PCCT platform device. This is purely used to represent
 *      the PCCT as a virtual device for registering with the
 *      generic Mailbox framework.
 *
 * @pdev: Pointer to platform device returned when a match
 *      is found.
 *
 *      Return: 0 for Success, else errno.
 */
static int pcc_mbox_probe(struct platform_device *pdev)
{
        int ret = 0;

        pcc_mbox_ctrl.chans = pcc_mbox_channels;
        pcc_mbox_ctrl.ops = &pcc_chan_ops;
        pcc_mbox_ctrl.dev = &pdev->dev;

        pr_info("Registering PCC driver as Mailbox controller\n");
        ret = mbox_controller_register(&pcc_mbox_ctrl);

        if (ret) {
                pr_err("Err registering PCC as Mailbox controller: %d\n", ret);
                ret = -ENODEV;
        }

        return ret;
}

struct platform_driver pcc_mbox_driver = {
        .probe = pcc_mbox_probe,
        .driver = {
                .name = "PCCT",
                .owner = THIS_MODULE,
        },
};

static int __init pcc_init(void)
{
        int ret;
        struct platform_device *pcc_pdev;

        if (acpi_disabled)
                return -ENODEV;

        /* Check if PCC support is available. */
        ret = acpi_pcc_probe();

        if (ret) {
                pr_debug("ACPI PCC probe failed.\n");
                return -ENODEV;
        }

        pcc_pdev = platform_create_bundle(&pcc_mbox_driver,
                        pcc_mbox_probe, NULL, 0, NULL, 0);

        if (IS_ERR(pcc_pdev)) {
                pr_debug("Err creating PCC platform bundle\n");
                return PTR_ERR(pcc_pdev);
        }

        return 0;
}
device_initcall(pcc_init);