// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2016 Google, Inc
 *
 * This device driver implements a TCG PTP FIFO interface over SPI for chips
 * with Cr50 firmware.
 * It is based on tpm_tis_spi driver by Peter Huewe and Christophe Ricard.
 */

#include <linux/completion.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/pm.h>
#include <linux/spi/spi.h>
#include <linux/wait.h>

#include "tpm_tis_core.h"
#include "tpm_tis_spi.h"

/*
 * Cr50 timing constants:
 * - can go to sleep not earlier than after CR50_SLEEP_DELAY_MSEC.
 * - needs up to CR50_WAKE_START_DELAY_USEC to wake after sleep.
 * - requires waiting for "ready" IRQ, if supported; or waiting for at least
 *   CR50_NOIRQ_ACCESS_DELAY_MSEC between transactions, if IRQ is not supported.
 * - waits for up to CR50_FLOW_CONTROL for flow control 'ready' indication.
 */
#define CR50_SLEEP_DELAY_MSEC                   1000
#define CR50_WAKE_START_DELAY_USEC              1000
#define CR50_NOIRQ_ACCESS_DELAY                 msecs_to_jiffies(2)
#define CR50_READY_IRQ_TIMEOUT                  msecs_to_jiffies(TPM2_TIMEOUT_A)
#define CR50_FLOW_CONTROL                       msecs_to_jiffies(TPM2_TIMEOUT_A)
#define MAX_IRQ_CONFIRMATION_ATTEMPTS           3

#define TPM_CR50_FW_VER(l)                      (0x0f90 | ((l) << 12))
#define TPM_CR50_MAX_FW_VER_LEN                 64

struct cr50_spi_phy {
        struct tpm_tis_spi_phy spi_phy;

        struct mutex time_track_mutex;
        unsigned long last_access;

        unsigned long access_delay;

        unsigned int irq_confirmation_attempt;
        bool irq_needs_confirmation;
        bool irq_confirmed;
};

static inline struct cr50_spi_phy *to_cr50_spi_phy(struct tpm_tis_spi_phy *phy)
{
        return container_of(phy, struct cr50_spi_phy, spi_phy);
}

/*
 * The cr50 interrupt handler just signals waiting threads that the
 * interrupt was asserted.  It does not do any processing triggered
 * by interrupts but is instead used to avoid fixed delays.
 */
static irqreturn_t cr50_spi_irq_handler(int dummy, void *dev_id)
{
        struct cr50_spi_phy *cr50_phy = dev_id;

        cr50_phy->irq_confirmed = true;
        complete(&cr50_phy->spi_phy.ready);

        return IRQ_HANDLED;
}

/*
 * Cr50 needs to have at least some delay between consecutive
 * transactions. Make sure we wait.
 */
static void cr50_ensure_access_delay(struct cr50_spi_phy *phy)
{
        unsigned long allowed_access = phy->last_access + phy->access_delay;
        unsigned long time_now = jiffies;
        struct device *dev = &phy->spi_phy.spi_device->dev;

        /*
         * Note: There is a small chance, if Cr50 is not accessed in a few days,
         * that time_in_range will not provide the correct result after the wrap
         * around for jiffies. In this case, we'll have an unneeded short delay,
         * which is fine.
         */
        if (time_in_range_open(time_now, phy->last_access, allowed_access)) {
                unsigned long remaining, timeout = allowed_access - time_now;

                remaining = wait_for_completion_timeout(&phy->spi_phy.ready,
                                                        timeout);
                if (!remaining && phy->irq_confirmed)
                        dev_warn(dev, "Timeout waiting for TPM ready IRQ\n");
        }

        if (phy->irq_needs_confirmation) {
                unsigned int attempt = ++phy->irq_confirmation_attempt;

                if (phy->irq_confirmed) {
                        phy->irq_needs_confirmation = false;
                        phy->access_delay = CR50_READY_IRQ_TIMEOUT;
                        dev_info(dev, "TPM ready IRQ confirmed on attempt %u\n",
                                 attempt);
                } else if (attempt > MAX_IRQ_CONFIRMATION_ATTEMPTS) {
                        phy->irq_needs_confirmation = false;
                        dev_warn(dev, "IRQ not confirmed - will use delays\n");
                }
        }
}

/*
 * Cr50 might go to sleep if there is no SPI activity for some time and
 * miss the first few bits/bytes on the bus. In such case, wake it up
 * by asserting CS and give it time to start up.
 */
static bool cr50_needs_waking(struct cr50_spi_phy *phy)
{
        /*
         * Note: There is a small chance, if Cr50 is not accessed in a few days,
         * that time_in_range will not provide the correct result after the wrap
         * around for jiffies. In this case, we'll probably timeout or read
         * incorrect value from TPM_STS and just retry the operation.
         */
        return !time_in_range_open(jiffies, phy->last_access,
                                   phy->spi_phy.wake_after);
}

static void cr50_wake_if_needed(struct cr50_spi_phy *cr50_phy)
{
        struct tpm_tis_spi_phy *phy = &cr50_phy->spi_phy;

        if (cr50_needs_waking(cr50_phy)) {
                /* Assert CS, wait 1 msec, deassert CS */
                struct spi_transfer spi_cs_wake = {
                        .delay = {
                                .value = 1000,
                                .unit = SPI_DELAY_UNIT_USECS
                        }
                };

                spi_sync_transfer(phy->spi_device, &spi_cs_wake, 1);
                /* Wait for it to fully wake */
                usleep_range(CR50_WAKE_START_DELAY_USEC,
                             CR50_WAKE_START_DELAY_USEC * 2);
        }

        /* Reset the time when we need to wake Cr50 again */
        phy->wake_after = jiffies + msecs_to_jiffies(CR50_SLEEP_DELAY_MSEC);
}

/*
 * Flow control: clock the bus and wait for cr50 to set LSB before
 * sending/receiving data. TCG PTP spec allows it to happen during
 * the last byte of header, but cr50 never does that in practice,
 * and earlier versions had a bug when it was set too early, so don't
 * check for it during header transfer.
 */
static int cr50_spi_flow_control(struct tpm_tis_spi_phy *phy,
                                 struct spi_transfer *spi_xfer)
{
        struct device *dev = &phy->spi_device->dev;
        unsigned long timeout = jiffies + CR50_FLOW_CONTROL;
        struct spi_message m;
        int ret;

        spi_xfer->len = 1;

        do {
                spi_message_init(&m);
                spi_message_add_tail(spi_xfer, &m);
                ret = spi_sync_locked(phy->spi_device, &m);
                if (ret < 0)
                        return ret;

                if (time_after(jiffies, timeout)) {
                        dev_warn(dev, "Timeout during flow control\n");
                        return -EBUSY;
                }
        } while (!(phy->iobuf[0] & 0x01));

        return 0;
}

static int tpm_tis_spi_cr50_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
                                     u8 *in, const u8 *out)
{
        struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
        struct cr50_spi_phy *cr50_phy = to_cr50_spi_phy(phy);
        int ret;

        mutex_lock(&cr50_phy->time_track_mutex);
        /*
         * Do this outside of spi_bus_lock in case cr50 is not the
         * only device on that spi bus.
         */
        cr50_ensure_access_delay(cr50_phy);
        cr50_wake_if_needed(cr50_phy);

        ret = tpm_tis_spi_transfer(data, addr, len, in, out);

        cr50_phy->last_access = jiffies;
        mutex_unlock(&cr50_phy->time_track_mutex);

        return ret;
}

static int tpm_tis_spi_cr50_read_bytes(struct tpm_tis_data *data, u32 addr,
                                       u16 len, u8 *result)
{
        return tpm_tis_spi_cr50_transfer(data, addr, len, result, NULL);
}

static int tpm_tis_spi_cr50_write_bytes(struct tpm_tis_data *data, u32 addr,
                                        u16 len, const u8 *value)
{
        return tpm_tis_spi_cr50_transfer(data, addr, len, NULL, value);
}

static const struct tpm_tis_phy_ops tpm_spi_cr50_phy_ops = {
        .read_bytes = tpm_tis_spi_cr50_read_bytes,
        .write_bytes = tpm_tis_spi_cr50_write_bytes,
        .read16 = tpm_tis_spi_read16,
        .read32 = tpm_tis_spi_read32,
        .write32 = tpm_tis_spi_write32,
};

static void cr50_print_fw_version(struct tpm_tis_data *data)
{
        struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
        int i, len = 0;
        char fw_ver[TPM_CR50_MAX_FW_VER_LEN + 1];
        char fw_ver_block[4];

        /*
         * Write anything to TPM_CR50_FW_VER to start from the beginning
         * of the version string
         */
        tpm_tis_write8(data, TPM_CR50_FW_VER(data->locality), 0);

        /* Read the string, 4 bytes at a time, until we get '\0' */
        do {
                tpm_tis_read_bytes(data, TPM_CR50_FW_VER(data->locality), 4,
                                   fw_ver_block);
                for (i = 0; i < 4 && fw_ver_block[i]; ++len, ++i)
                        fw_ver[len] = fw_ver_block[i];
        } while (i == 4 && len < TPM_CR50_MAX_FW_VER_LEN);
        fw_ver[len] = '\0';

        dev_info(&phy->spi_device->dev, "Cr50 firmware version: %s\n", fw_ver);
}

int cr50_spi_probe(struct spi_device *spi)
{
        struct tpm_tis_spi_phy *phy;
        struct cr50_spi_phy *cr50_phy;
        int ret;
        struct tpm_chip *chip;

        cr50_phy = devm_kzalloc(&spi->dev, sizeof(*cr50_phy), GFP_KERNEL);
        if (!cr50_phy)
                return -ENOMEM;

        phy = &cr50_phy->spi_phy;
        phy->flow_control = cr50_spi_flow_control;
        phy->wake_after = jiffies;
        init_completion(&phy->ready);

        cr50_phy->access_delay = CR50_NOIRQ_ACCESS_DELAY;
        cr50_phy->last_access = jiffies;
        mutex_init(&cr50_phy->time_track_mutex);

        if (spi->irq > 0) {
                ret = devm_request_irq(&spi->dev, spi->irq,
                                       cr50_spi_irq_handler,
                                       IRQF_TRIGGER_RISING | IRQF_ONESHOT,
                                       "cr50_spi", cr50_phy);
                if (ret < 0) {
                        if (ret == -EPROBE_DEFER)
                                return ret;
                        dev_warn(&spi->dev, "Requesting IRQ %d failed: %d\n",
                                 spi->irq, ret);
                        /*
                         * This is not fatal, the driver will fall back to
                         * delays automatically, since ready will never
                         * be completed without a registered irq handler.
                         * So, just fall through.
                         */
                } else {
                        /*
                         * IRQ requested, let's verify that it is actually
                         * triggered, before relying on it.
                         */
                        cr50_phy->irq_needs_confirmation = true;
                }
        } else {
                dev_warn(&spi->dev,
                         "No IRQ - will use delays between transactions.\n");
        }

        ret = tpm_tis_spi_init(spi, phy, -1, &tpm_spi_cr50_phy_ops);
        if (ret)
                return ret;

        cr50_print_fw_version(&phy->priv);

        chip = dev_get_drvdata(&spi->dev);
        chip->flags |= TPM_CHIP_FLAG_FIRMWARE_POWER_MANAGED;

        return 0;
}

#ifdef CONFIG_PM_SLEEP
int tpm_tis_spi_resume(struct device *dev)
{
        struct tpm_chip *chip = dev_get_drvdata(dev);
        struct tpm_tis_data *data = dev_get_drvdata(&chip->dev);
        struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
        /*
         * Jiffies not increased during suspend, so we need to reset
         * the time to wake Cr50 after resume.
         */
        phy->wake_after = jiffies;

        return tpm_tis_resume(dev);
}
#endif