// SPDX-License-Identifier: GPL-2.0
/*
 *  i2c slave support for Atmel's AT91 Two-Wire Interface (TWI)
 *
 *  Copyright (C) 2017 Juergen Fitschen <me@jue.yt>
 */

#include <linux/err.h>
#include <linux/i2c.h>
#include <linux/interrupt.h>
#include <linux/pm_runtime.h>

#include "i2c-at91.h"

static irqreturn_t atmel_twi_interrupt_slave(int irq, void *dev_id)
{
        struct at91_twi_dev *dev = dev_id;
        const unsigned status = at91_twi_read(dev, AT91_TWI_SR);
        const unsigned irqstatus = status & at91_twi_read(dev, AT91_TWI_IMR);
        u8 value;

        if (!irqstatus)
                return IRQ_NONE;

        /* slave address has been detected on I2C bus */
        if (irqstatus & AT91_TWI_SVACC) {
                if (status & AT91_TWI_SVREAD) {
                        i2c_slave_event(dev->slave,
                                        I2C_SLAVE_READ_REQUESTED, &value);
                        writeb_relaxed(value, dev->base + AT91_TWI_THR);
                        at91_twi_write(dev, AT91_TWI_IER,
                                       AT91_TWI_TXRDY | AT91_TWI_EOSACC);
                } else {
                        i2c_slave_event(dev->slave,
                                        I2C_SLAVE_WRITE_REQUESTED, &value);
                        at91_twi_write(dev, AT91_TWI_IER,
                                       AT91_TWI_RXRDY | AT91_TWI_EOSACC);
                }
                at91_twi_write(dev, AT91_TWI_IDR, AT91_TWI_SVACC);
        }

        /* byte transmitted to remote master */
        if (irqstatus & AT91_TWI_TXRDY) {
                i2c_slave_event(dev->slave, I2C_SLAVE_READ_PROCESSED, &value);
                writeb_relaxed(value, dev->base + AT91_TWI_THR);
        }

        /* byte received from remote master */
        if (irqstatus & AT91_TWI_RXRDY) {
                value = readb_relaxed(dev->base + AT91_TWI_RHR);
                i2c_slave_event(dev->slave, I2C_SLAVE_WRITE_RECEIVED, &value);
        }

        /* master sent stop */
        if (irqstatus & AT91_TWI_EOSACC) {
                at91_twi_write(dev, AT91_TWI_IDR,
                               AT91_TWI_TXRDY | AT91_TWI_RXRDY | AT91_TWI_EOSACC);
                at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_SVACC);
                i2c_slave_event(dev->slave, I2C_SLAVE_STOP, &value);
        }

        return IRQ_HANDLED;
}

static int at91_reg_slave(struct i2c_client *slave)
{
        struct at91_twi_dev *dev = i2c_get_adapdata(slave->adapter);

        if (dev->slave)
                return -EBUSY;

        if (slave->flags & I2C_CLIENT_TEN)
                return -EAFNOSUPPORT;

        /* Make sure twi_clk doesn't get turned off! */
        pm_runtime_get_sync(dev->dev);

        dev->slave = slave;
        dev->smr = AT91_TWI_SMR_SADR(slave->addr);

        at91_init_twi_bus(dev);
        at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_SVACC);

        dev_info(dev->dev, "entered slave mode (ADR=%d)\n", slave->addr);

        return 0;
}

static int at91_unreg_slave(struct i2c_client *slave)
{
        struct at91_twi_dev *dev = i2c_get_adapdata(slave->adapter);

        WARN_ON(!dev->slave);

        dev_info(dev->dev, "leaving slave mode\n");

        dev->slave = NULL;
        dev->smr = 0;

        at91_init_twi_bus(dev);

        pm_runtime_put(dev->dev);

        return 0;
}

static u32 at91_twi_func(struct i2c_adapter *adapter)
{
        return I2C_FUNC_SLAVE;
}

static const struct i2c_algorithm at91_twi_algorithm_slave = {
        .reg_slave      = at91_reg_slave,
        .unreg_slave    = at91_unreg_slave,
        .functionality  = at91_twi_func,
};

int at91_twi_probe_slave(struct platform_device *pdev,
                         u32 phy_addr, struct at91_twi_dev *dev)
{
        int rc;

        rc = devm_request_irq(&pdev->dev, dev->irq, atmel_twi_interrupt_slave,
                              0, dev_name(dev->dev), dev);
        if (rc) {
                dev_err(dev->dev, "Cannot get irq %d: %d\n", dev->irq, rc);
                return rc;
        }

        dev->adapter.algo = &at91_twi_algorithm_slave;

        return 0;
}

void at91_init_twi_bus_slave(struct at91_twi_dev *dev)
{
        at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_MSDIS);
        if (dev->slave_detected && dev->smr) {
                at91_twi_write(dev, AT91_TWI_SMR, dev->smr);
                at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SVEN);
        }
}