// SPDX-License-Identifier: GPL-2.0

#include <linux/i2c.h>
#include <linux/pci.h>
#include <linux/psp-platform-access.h>
#include <linux/psp.h>
#include <linux/workqueue.h>

#include "i2c-designware-core.h"

#define PSP_I2C_RESERVATION_TIME_MS 100

#define PSP_I2C_REQ_RETRY_CNT           400
#define PSP_I2C_REQ_RETRY_DELAY_US      (25 * USEC_PER_MSEC)
#define PSP_I2C_REQ_STS_OK              0x0
#define PSP_I2C_REQ_STS_BUS_BUSY        0x1
#define PSP_I2C_REQ_STS_INV_PARAM       0x3

enum psp_i2c_req_type {
        PSP_I2C_REQ_ACQUIRE,
        PSP_I2C_REQ_RELEASE,
        PSP_I2C_REQ_MAX
};

struct psp_i2c_req {
        struct psp_req_buffer_hdr hdr;
        enum psp_i2c_req_type type;
};

static DEFINE_MUTEX(psp_i2c_access_mutex);
static unsigned long psp_i2c_sem_acquired;
static u32 psp_i2c_access_count;
static bool psp_i2c_mbox_fail;
static struct device *psp_i2c_dev;

static int (*_psp_send_i2c_req)(struct psp_i2c_req *req);

/* Helper to verify status returned by PSP */
static int check_i2c_req_sts(struct psp_i2c_req *req)
{
        u32 status;

        /* Status field in command-response buffer is updated by PSP */
        status = READ_ONCE(req->hdr.status);

        switch (status) {
        case PSP_I2C_REQ_STS_OK:
                return 0;
        case PSP_I2C_REQ_STS_BUS_BUSY:
                return -EBUSY;
        case PSP_I2C_REQ_STS_INV_PARAM:
        default:
                return -EIO;
        }
}

/*
 * Errors in x86-PSP i2c-arbitration protocol may occur at two levels:
 * 1. mailbox communication - PSP is not operational or some IO errors with
 *    basic communication had happened.
 * 2. i2c-requests - PSP refuses to grant i2c arbitration to x86 for too long.
 *
 * In order to distinguish between these in error handling code all mailbox
 * communication errors on the first level (from CCP symbols) will be passed
 * up and if -EIO is returned the second level will be checked.
 */
static int psp_send_i2c_req_cezanne(struct psp_i2c_req *req)
{
        int ret;

        ret = psp_send_platform_access_msg(PSP_I2C_REQ_BUS_CMD, (struct psp_request *)req);
        if (ret == -EIO)
                return check_i2c_req_sts(req);

        return ret;
}

static int psp_send_i2c_req_doorbell(struct psp_i2c_req *req)
{
        int ret;

        ret = psp_ring_platform_doorbell(req->type, &req->hdr.status);
        if (ret == -EIO)
                return check_i2c_req_sts(req);

        return ret;
}

static int psp_send_i2c_req(enum psp_i2c_req_type i2c_req_type)
{
        struct psp_i2c_req *req;
        unsigned long start;
        int status, ret;

        /* Allocate command-response buffer */
        req = kzalloc_obj(*req);
        if (!req)
                return -ENOMEM;

        req->hdr.payload_size = sizeof(*req);
        req->type = i2c_req_type;

        start = jiffies;
        ret = read_poll_timeout(_psp_send_i2c_req, status,
                                (status != -EBUSY),
                                PSP_I2C_REQ_RETRY_DELAY_US,
                                PSP_I2C_REQ_RETRY_CNT * PSP_I2C_REQ_RETRY_DELAY_US,
                                0, req);
        if (ret) {
                dev_err(psp_i2c_dev, "Timed out waiting for PSP to %s I2C bus\n",
                        (i2c_req_type == PSP_I2C_REQ_ACQUIRE) ?
                        "release" : "acquire");
                goto cleanup;
        }

        ret = status;
        if (ret) {
                dev_err(psp_i2c_dev, "PSP communication error\n");
                goto cleanup;
        }

        dev_dbg(psp_i2c_dev, "Request accepted by PSP after %ums\n",
                jiffies_to_msecs(jiffies - start));

cleanup:
        if (ret) {
                dev_err(psp_i2c_dev, "Assume i2c bus is for exclusive host usage\n");
                psp_i2c_mbox_fail = true;
        }

        kfree(req);
        return ret;
}

static void release_bus(void)
{
        int status;

        if (!psp_i2c_sem_acquired)
                return;

        status = psp_send_i2c_req(PSP_I2C_REQ_RELEASE);
        if (status)
                return;

        dev_dbg(psp_i2c_dev, "PSP semaphore held for %ums\n",
                jiffies_to_msecs(jiffies - psp_i2c_sem_acquired));

        psp_i2c_sem_acquired = 0;
}

static void psp_release_i2c_bus_deferred(struct work_struct *work)
{
        guard(mutex)(&psp_i2c_access_mutex);

        /*
         * If there is any pending transaction, cannot release the bus here.
         * psp_release_i2c_bus() will take care of this later.
         */
        if (psp_i2c_access_count)
                return;

        release_bus();
}
static DECLARE_DELAYED_WORK(release_queue, psp_release_i2c_bus_deferred);

static int psp_acquire_i2c_bus(void)
{
        int status;

        guard(mutex)(&psp_i2c_access_mutex);

        /* Return early if mailbox malfunctioned */
        if (psp_i2c_mbox_fail)
                return 0;

        psp_i2c_access_count++;

        /*
         * No need to request bus arbitration once we are inside semaphore
         * reservation period.
         */
        if (psp_i2c_sem_acquired)
                return 0;

        status = psp_send_i2c_req(PSP_I2C_REQ_ACQUIRE);
        if (status)
                return 0;

        psp_i2c_sem_acquired = jiffies;

        schedule_delayed_work(&release_queue,
                              msecs_to_jiffies(PSP_I2C_RESERVATION_TIME_MS));

        /*
         * In case of errors with PSP arbitrator psp_i2c_mbox_fail variable is
         * set above. As a consequence consecutive calls to acquire will bypass
         * communication with PSP. At any case i2c bus is granted to the caller,
         * thus always return success.
         */
        return 0;
}

static void psp_release_i2c_bus(void)
{
        guard(mutex)(&psp_i2c_access_mutex);

        /* Return early if mailbox was malfunctioned */
        if (psp_i2c_mbox_fail)
                return;

        /*
         * If we are last owner of PSP semaphore, need to release arbitration
         * via mailbox.
         */
        psp_i2c_access_count--;
        if (psp_i2c_access_count)
                return;

        /*
         * Send a release command to PSP if the semaphore reservation timeout
         * elapsed but x86 still owns the controller.
         */
        if (!delayed_work_pending(&release_queue))
                release_bus();
}

/*
 * Locking methods are based on the default implementation from
 * drivers/i2c/i2c-core-base.c, but with PSP acquire and release operations
 * added. With this in place we can ensure that i2c clients on the bus shared
 * with PSP are able to lock HW access to the bus for arbitrary number of
 * operations - that is e.g. write-wait-read.
 */
static void i2c_adapter_dw_psp_lock_bus(struct i2c_adapter *adapter,
                                        unsigned int flags)
{
        psp_acquire_i2c_bus();
        rt_mutex_lock_nested(&adapter->bus_lock, i2c_adapter_depth(adapter));
}

static int i2c_adapter_dw_psp_trylock_bus(struct i2c_adapter *adapter,
                                          unsigned int flags)
{
        int ret;

        ret = rt_mutex_trylock(&adapter->bus_lock);
        if (ret)
                return ret;

        psp_acquire_i2c_bus();

        return ret;
}

static void i2c_adapter_dw_psp_unlock_bus(struct i2c_adapter *adapter,
                                          unsigned int flags)
{
        psp_release_i2c_bus();
        rt_mutex_unlock(&adapter->bus_lock);
}

static const struct i2c_lock_operations i2c_dw_psp_lock_ops = {
        .lock_bus = i2c_adapter_dw_psp_lock_bus,
        .trylock_bus = i2c_adapter_dw_psp_trylock_bus,
        .unlock_bus = i2c_adapter_dw_psp_unlock_bus,
};

int i2c_dw_amdpsp_probe_lock_support(struct dw_i2c_dev *dev)
{
        struct pci_dev *rdev;

        if (!IS_REACHABLE(CONFIG_CRYPTO_DEV_CCP_DD))
                return -ENODEV;

        if (!dev)
                return -ENODEV;

        if (!(dev->flags & ARBITRATION_SEMAPHORE))
                return -ENODEV;

        /* Allow to bind only one instance of a driver */
        if (psp_i2c_dev)
                return -EEXIST;

        /* Cezanne uses platform mailbox, Mendocino and later use doorbell */
        rdev = pci_get_domain_bus_and_slot(0, 0, PCI_DEVFN(0, 0));
        if (rdev->device == 0x1630)
                _psp_send_i2c_req = psp_send_i2c_req_cezanne;
        else
                _psp_send_i2c_req = psp_send_i2c_req_doorbell;
        pci_dev_put(rdev);

        if (psp_check_platform_access_status())
                return -EPROBE_DEFER;

        psp_i2c_dev = dev->dev;

        dev_info(psp_i2c_dev, "I2C bus managed by AMD PSP\n");

        /*
         * Install global locking callbacks for adapter as well as internal i2c
         * controller locks.
         */
        dev->adapter.lock_ops = &i2c_dw_psp_lock_ops;
        dev->acquire_lock = psp_acquire_i2c_bus;
        dev->release_lock = psp_release_i2c_bus;

        return 0;
}