i2c-bcm2835.c

// SPDX-License-Identifier: GPL-2.0
/*
 * BCM2835 master mode driver
 */

#include <linux/clk.h>
#include <linux/clkdev.h>
#include <linux/clk-provider.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/i2c.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/module.h>
#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

#define BCM2835_I2C_C		0x0
#define BCM2835_I2C_S		0x4
#define BCM2835_I2C_DLEN	0x8
#define BCM2835_I2C_A		0xc
#define BCM2835_I2C_FIFO	0x10
#define BCM2835_I2C_DIV		0x14
#define BCM2835_I2C_DEL		0x18
/*
 * 16-bit field for the number of SCL cycles to wait after rising SCL
 * before deciding the slave is not responding. 0 disables the
 * timeout detection.
 */
#define BCM2835_I2C_CLKT	0x1c

#define BCM2835_I2C_C_READ	BIT(0)
#define BCM2835_I2C_C_CLEAR	BIT(4) /* bits 4 and 5 both clear */
#define BCM2835_I2C_C_ST	BIT(7)
#define BCM2835_I2C_C_INTD	BIT(8)
#define BCM2835_I2C_C_INTT	BIT(9)
#define BCM2835_I2C_C_INTR	BIT(10)
#define BCM2835_I2C_C_I2CEN	BIT(15)

#define BCM2835_I2C_S_TA	BIT(0)
#define BCM2835_I2C_S_DONE	BIT(1)
#define BCM2835_I2C_S_TXW	BIT(2)
#define BCM2835_I2C_S_RXR	BIT(3)
#define BCM2835_I2C_S_TXD	BIT(4)
#define BCM2835_I2C_S_RXD	BIT(5)
#define BCM2835_I2C_S_TXE	BIT(6)
#define BCM2835_I2C_S_RXF	BIT(7)
#define BCM2835_I2C_S_ERR	BIT(8)
#define BCM2835_I2C_S_CLKT	BIT(9)
#define BCM2835_I2C_S_LEN	BIT(10) /* Fake bit for SW error reporting */

#define BCM2835_I2C_FEDL_SHIFT	16
#define BCM2835_I2C_REDL_SHIFT	0

#define BCM2835_I2C_CDIV_MIN	0x0002
#define BCM2835_I2C_CDIV_MAX	0xFFFE

struct bcm2835_i2c_dev {
	struct device *dev;
	void __iomem *regs;
	int irq;
	struct i2c_adapter adapter;
	struct completion completion;
	struct i2c_msg *curr_msg;
	struct clk *bus_clk;
	int num_msgs;
	u32 msg_err;
	u8 *msg_buf;
	size_t msg_buf_remaining;
};

static inline void bcm2835_i2c_writel(struct bcm2835_i2c_dev *i2c_dev,
				      u32 reg, u32 val)
{
	writel(val, i2c_dev->regs + reg);
}

static inline u32 bcm2835_i2c_readl(struct bcm2835_i2c_dev *i2c_dev, u32 reg)
{
	return readl(i2c_dev->regs + reg);
}

#define to_clk_bcm2835_i2c(_hw) container_of(_hw, struct clk_bcm2835_i2c, hw)
struct clk_bcm2835_i2c {
	struct clk_hw hw;
	struct bcm2835_i2c_dev *i2c_dev;
};

static int clk_bcm2835_i2c_calc_divider(unsigned long rate,
				unsigned long parent_rate)
{
	u32 divider = DIV_ROUND_UP(parent_rate, rate);

	/*
	 * Per the datasheet, the register is always interpreted as an even
	 * number, by rounding down. In other words, the LSB is ignored. So,
	 * if the LSB is set, increment the divider to avoid any issue.
	 */
	if (divider & 1)
		divider++;
	if ((divider < BCM2835_I2C_CDIV_MIN) ||
	    (divider > BCM2835_I2C_CDIV_MAX))
		return -EINVAL;

	return divider;
}

static int clk_bcm2835_i2c_set_rate(struct clk_hw *hw, unsigned long rate,
				unsigned long parent_rate)
{
	struct clk_bcm2835_i2c *div = to_clk_bcm2835_i2c(hw);
	u32 redl, fedl;
	u32 divider = clk_bcm2835_i2c_calc_divider(rate, parent_rate);

	if (divider == -EINVAL)
		return -EINVAL;

	bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_DIV, divider);

	/*
	 * Number of core clocks to wait after falling edge before
	 * outputting the next data bit.  Note that both FEDL and REDL
	 * can't be greater than CDIV/2.
	 */
	fedl = max(divider / 16, 1u);

	/*
	 * Number of core clocks to wait after rising edge before
	 * sampling the next incoming data bit.
	 */
	redl = max(divider / 4, 1u);

	bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_DEL,
			   (fedl << BCM2835_I2C_FEDL_SHIFT) |
			   (redl << BCM2835_I2C_REDL_SHIFT));
	return 0;
}

static long clk_bcm2835_i2c_round_rate(struct clk_hw *hw, unsigned long rate,
				unsigned long *parent_rate)
{
	u32 divider = clk_bcm2835_i2c_calc_divider(rate, *parent_rate);

	return DIV_ROUND_UP(*parent_rate, divider);
}

static unsigned long clk_bcm2835_i2c_recalc_rate(struct clk_hw *hw,
						unsigned long parent_rate)
{
	struct clk_bcm2835_i2c *div = to_clk_bcm2835_i2c(hw);
	u32 divider = bcm2835_i2c_readl(div->i2c_dev, BCM2835_I2C_DIV);

	return DIV_ROUND_UP(parent_rate, divider);
}

static const struct clk_ops clk_bcm2835_i2c_ops = {
	.set_rate = clk_bcm2835_i2c_set_rate,
	.round_rate = clk_bcm2835_i2c_round_rate,
	.recalc_rate = clk_bcm2835_i2c_recalc_rate,
};

static struct clk *bcm2835_i2c_register_div(struct device *dev,
					struct clk *mclk,
					struct bcm2835_i2c_dev *i2c_dev)
{
	struct clk_init_data init;
	struct clk_bcm2835_i2c *priv;
	char name[32];
	const char *mclk_name;

	snprintf(name, sizeof(name), "%s_div", dev_name(dev));

	mclk_name = __clk_get_name(mclk);

	init.ops = &clk_bcm2835_i2c_ops;
	init.name = name;
	init.parent_names = (const char* []) { mclk_name };
	init.num_parents = 1;
	init.flags = 0;

	priv = devm_kzalloc(dev, sizeof(struct clk_bcm2835_i2c), GFP_KERNEL);
	if (priv == NULL)
		return ERR_PTR(-ENOMEM);

	priv->hw.init = &init;
	priv->i2c_dev = i2c_dev;

	clk_hw_register_clkdev(&priv->hw, "div", dev_name(dev));
	return devm_clk_register(dev, &priv->hw);
}

static void bcm2835_fill_txfifo(struct bcm2835_i2c_dev *i2c_dev)
{
	u32 val;

	while (i2c_dev->msg_buf_remaining) {
		val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
		if (!(val & BCM2835_I2C_S_TXD))
			break;
		bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_FIFO,
				   *i2c_dev->msg_buf);
		i2c_dev->msg_buf++;
		i2c_dev->msg_buf_remaining--;
	}
}

static void bcm2835_drain_rxfifo(struct bcm2835_i2c_dev *i2c_dev)
{
	u32 val;

	while (i2c_dev->msg_buf_remaining) {
		val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
		if (!(val & BCM2835_I2C_S_RXD))
			break;
		*i2c_dev->msg_buf = bcm2835_i2c_readl(i2c_dev,
						      BCM2835_I2C_FIFO);
		i2c_dev->msg_buf++;
		i2c_dev->msg_buf_remaining--;
	}
}

/*
 * Repeated Start Condition (Sr)
 * The BCM2835 ARM Peripherals datasheet mentions a way to trigger a Sr when it
 * talks about reading from a slave with 10 bit address. This is achieved by
 * issuing a write, poll the I2CS.TA flag and wait for it to be set, and then
 * issue a read.
 * A comment in https://github.com/raspberrypi/linux/issues/254 shows how the
 * firmware actually does it using polling and says that it's a workaround for
 * a problem in the state machine.
 * It turns out that it is possible to use the TXW interrupt to know when the
 * transfer is active, provided the FIFO has not been prefilled.
 */

static void bcm2835_i2c_start_transfer(struct bcm2835_i2c_dev *i2c_dev)
{
	u32 c = BCM2835_I2C_C_ST | BCM2835_I2C_C_I2CEN;
	struct i2c_msg *msg = i2c_dev->curr_msg;
	bool last_msg = (i2c_dev->num_msgs == 1);

	if (!i2c_dev->num_msgs)
		return;

	i2c_dev->num_msgs--;
	i2c_dev->msg_buf = msg->buf;
	i2c_dev->msg_buf_remaining = msg->len;

	if (msg->flags & I2C_M_RD)
		c |= BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
	else
		c |= BCM2835_I2C_C_INTT;

	if (last_msg)
		c |= BCM2835_I2C_C_INTD;

	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_A, msg->addr);
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DLEN, msg->len);
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
}

static void bcm2835_i2c_finish_transfer(struct bcm2835_i2c_dev *i2c_dev)
{
	i2c_dev->curr_msg = NULL;
	i2c_dev->num_msgs = 0;

	i2c_dev->msg_buf = NULL;
	i2c_dev->msg_buf_remaining = 0;
}

/*
 * Note about I2C_C_CLEAR on error:
 * The I2C_C_CLEAR on errors will take some time to resolve -- if you were in
 * non-idle state and I2C_C_READ, it sets an abort_rx flag and runs through
 * the state machine to send a NACK and a STOP. Since we're setting CLEAR
 * without I2CEN, that NACK will be hanging around queued up for next time
 * we start the engine.
 */

static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
{
	struct bcm2835_i2c_dev *i2c_dev = data;
	u32 val, err;

	val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);

	err = val & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
	if (err) {
		i2c_dev->msg_err = err;
		goto complete;
	}

	if (val & BCM2835_I2C_S_DONE) {
		if (!i2c_dev->curr_msg) {
			dev_err(i2c_dev->dev, "Got unexpected interrupt (from firmware?)\n");
		} else if (i2c_dev->curr_msg->flags & I2C_M_RD) {
			bcm2835_drain_rxfifo(i2c_dev);
			val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
		}

		if ((val & BCM2835_I2C_S_RXD) || i2c_dev->msg_buf_remaining)
			i2c_dev->msg_err = BCM2835_I2C_S_LEN;
		else
			i2c_dev->msg_err = 0;
		goto complete;
	}

	if (val & BCM2835_I2C_S_TXW) {
		if (!i2c_dev->msg_buf_remaining) {
			i2c_dev->msg_err = val | BCM2835_I2C_S_LEN;
			goto complete;
		}

		bcm2835_fill_txfifo(i2c_dev);

		if (i2c_dev->num_msgs && !i2c_dev->msg_buf_remaining) {
			i2c_dev->curr_msg++;
			bcm2835_i2c_start_transfer(i2c_dev);
		}

		return IRQ_HANDLED;
	}

	if (val & BCM2835_I2C_S_RXR) {
		if (!i2c_dev->msg_buf_remaining) {
			i2c_dev->msg_err = val | BCM2835_I2C_S_LEN;
			goto complete;
		}

		bcm2835_drain_rxfifo(i2c_dev);
		return IRQ_HANDLED;
	}

	return IRQ_NONE;

complete:
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, BCM2835_I2C_S_CLKT |
			   BCM2835_I2C_S_ERR | BCM2835_I2C_S_DONE);
	complete(&i2c_dev->completion);

	return IRQ_HANDLED;
}

static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
			    int num)
{
	struct bcm2835_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
	unsigned long time_left;
	int i;

	for (i = 0; i < (num - 1); i++)
		if (msgs[i].flags & I2C_M_RD) {
			dev_warn_once(i2c_dev->dev,
				      "only one read message supported, has to be last\n");
			return -EOPNOTSUPP;
		}

	i2c_dev->curr_msg = msgs;
	i2c_dev->num_msgs = num;
	reinit_completion(&i2c_dev->completion);

	bcm2835_i2c_start_transfer(i2c_dev);

	time_left = wait_for_completion_timeout(&i2c_dev->completion,
						adap->timeout);

	bcm2835_i2c_finish_transfer(i2c_dev);

	if (!time_left) {
		bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C,
				   BCM2835_I2C_C_CLEAR);
		dev_err(i2c_dev->dev, "i2c transfer timed out\n");
		return -ETIMEDOUT;
	}

	if (!i2c_dev->msg_err)
		return num;

	dev_dbg(i2c_dev->dev, "i2c transfer failed: %x\n", i2c_dev->msg_err);

	if (i2c_dev->msg_err & BCM2835_I2C_S_ERR)
		return -EREMOTEIO;

	return -EIO;
}

static u32 bcm2835_i2c_func(struct i2c_adapter *adap)
{
	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
}

static const struct i2c_algorithm bcm2835_i2c_algo = {
	.master_xfer	= bcm2835_i2c_xfer,
	.functionality	= bcm2835_i2c_func,
};

/*
 * The BCM2835 was reported to have problems with clock stretching:
 * https://www.advamation.com/knowhow/raspberrypi/rpi-i2c-bug.html
 * https://www.raspberrypi.org/forums/viewtopic.php?p=146272
 */
static const struct i2c_adapter_quirks bcm2835_i2c_quirks = {
	.flags = I2C_AQ_NO_CLK_STRETCH,
};

static int bcm2835_i2c_probe(struct platform_device *pdev)
{
	struct bcm2835_i2c_dev *i2c_dev;
	struct resource *mem, *irq;
	int ret;
	struct i2c_adapter *adap;
	struct clk *mclk;
	u32 bus_clk_rate;

	i2c_dev = devm_kzalloc(&pdev->dev, sizeof(*i2c_dev), GFP_KERNEL);
	if (!i2c_dev)
		return -ENOMEM;
	platform_set_drvdata(pdev, i2c_dev);
	i2c_dev->dev = &pdev->dev;
	init_completion(&i2c_dev->completion);

	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	i2c_dev->regs = devm_ioremap_resource(&pdev->dev, mem);
	if (IS_ERR(i2c_dev->regs))
		return PTR_ERR(i2c_dev->regs);

	mclk = devm_clk_get(&pdev->dev, NULL);
	if (IS_ERR(mclk))
		return dev_err_probe(&pdev->dev, PTR_ERR(mclk),
				     "Could not get clock\n");

	i2c_dev->bus_clk = bcm2835_i2c_register_div(&pdev->dev, mclk, i2c_dev);

	if (IS_ERR(i2c_dev->bus_clk)) {
		dev_err(&pdev->dev, "Could not register clock\n");
		return PTR_ERR(i2c_dev->bus_clk);
	}

	ret = of_property_read_u32(pdev->dev.of_node, "clock-frequency",
				   &bus_clk_rate);
	if (ret < 0) {
		dev_warn(&pdev->dev,
			 "Could not read clock-frequency property\n");
		bus_clk_rate = I2C_MAX_STANDARD_MODE_FREQ;
	}

	ret = clk_set_rate_exclusive(i2c_dev->bus_clk, bus_clk_rate);
	if (ret < 0) {
		dev_err(&pdev->dev, "Could not set clock frequency\n");
		return ret;
	}

	ret = clk_prepare_enable(i2c_dev->bus_clk);
	if (ret) {
		dev_err(&pdev->dev, "Couldn't prepare clock");
		return ret;
	}

	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
	if (!irq) {
		dev_err(&pdev->dev, "No IRQ resource\n");
		return -ENODEV;
	}
	i2c_dev->irq = irq->start;

	ret = request_irq(i2c_dev->irq, bcm2835_i2c_isr, IRQF_SHARED,
			  dev_name(&pdev->dev), i2c_dev);
	if (ret) {
		dev_err(&pdev->dev, "Could not request IRQ\n");
		return -ENODEV;
	}

	adap = &i2c_dev->adapter;
	i2c_set_adapdata(adap, i2c_dev);
	adap->owner = THIS_MODULE;
	adap->class = I2C_CLASS_DEPRECATED;
	snprintf(adap->name, sizeof(adap->name), "bcm2835 (%s)",
		 of_node_full_name(pdev->dev.of_node));
	adap->algo = &bcm2835_i2c_algo;
	adap->dev.parent = &pdev->dev;
	adap->dev.of_node = pdev->dev.of_node;
	adap->quirks = of_device_get_match_data(&pdev->dev);

	/*
	 * Disable the hardware clock stretching timeout. SMBUS
	 * specifies a limit for how long the device can stretch the
	 * clock, but core I2C doesn't.
	 */
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_CLKT, 0);
	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, 0);

	ret = i2c_add_adapter(adap);
	if (ret)
		free_irq(i2c_dev->irq, i2c_dev);

	return ret;
}

static int bcm2835_i2c_remove(struct platform_device *pdev)
{
	struct bcm2835_i2c_dev *i2c_dev = platform_get_drvdata(pdev);

	clk_rate_exclusive_put(i2c_dev->bus_clk);
	clk_disable_unprepare(i2c_dev->bus_clk);

	free_irq(i2c_dev->irq, i2c_dev);
	i2c_del_adapter(&i2c_dev->adapter);

	return 0;
}

static const struct of_device_id bcm2835_i2c_of_match[] = {
	{ .compatible = "brcm,bcm2711-i2c" },
	{ .compatible = "brcm,bcm2835-i2c", .data = &bcm2835_i2c_quirks },
	{},
};
MODULE_DEVICE_TABLE(of, bcm2835_i2c_of_match);

static struct platform_driver bcm2835_i2c_driver = {
	.probe		= bcm2835_i2c_probe,
	.remove		= bcm2835_i2c_remove,
	.driver		= {
		.name	= "i2c-bcm2835",
		.of_match_table = bcm2835_i2c_of_match,
	},
};
module_platform_driver(bcm2835_i2c_driver);

MODULE_AUTHOR("Stephen Warren <swarren@wwwdotorg.org>");
MODULE_DESCRIPTION("BCM2835 I2C bus adapter");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform:i2c-bcm2835");