i2c: add bcm2835 driver

This implements a very basic I2C host driver for the BCM2835 SoC. Missing
features so far are:

* 10-bit addressing.
* DMA.

Reviewed-by: Grant Likely <[e-mail]>
Signed-off-by: Stephen Warren <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

Documentation/devicetree/bindings/i2c/brcm,bcm2835-i2c.txt

···
+Broadcom BCM2835 I2C controller
+
+Required properties:
+- compatible : Should be "brcm,bcm2835-i2c".
+- reg: Should contain register location and length.
+- interrupts: Should contain interrupt.
+- clocks : The clock feeding the I2C controller.
+
+Recommended properties:
+- clock-frequency : desired I2C bus clock frequency in Hz.
+
+Example:
+
+i2c@20205000 {
+	compatible = "brcm,bcm2835-i2c";
+	reg = <0x7e205000 0x1000>;
+	interrupts = <2 21>;
+	clocks = <&clk_i2c>;
+	clock-frequency = <100000>;
+};

drivers/i2c/busses/Kconfig

···
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-au1550.
 
+config I2C_BCM2835
+	tristate "Broadcom BCM2835 I2C controller"
+	depends on ARCH_BCM2835
+	help
+	  If you say yes to this option, support will be included for the
+	  BCM2835 I2C controller.
+
+	  If you don't know what to do here, say N.
+
+	  This support is also available as a module.  If so, the module
+	  will be called i2c-bcm2835.
+
 config I2C_BLACKFIN_TWI
 	tristate "Blackfin TWI I2C support"
 	depends on BLACKFIN

drivers/i2c/busses/Makefile

···
 # Embedded system I2C/SMBus host controller drivers
 obj-$(CONFIG_I2C_AT91)		+= i2c-at91.o
 obj-$(CONFIG_I2C_AU1550)	+= i2c-au1550.o
+obj-$(CONFIG_I2C_BCM2835)	+= i2c-bcm2835.o
 obj-$(CONFIG_I2C_BLACKFIN_TWI)	+= i2c-bfin-twi.o
 obj-$(CONFIG_I2C_CBUS_GPIO)	+= i2c-cbus-gpio.o
 obj-$(CONFIG_I2C_CPM)		+= i2c-cpm.o

drivers/i2c/busses/i2c-bcm2835.c

···
+/*
+ * BCM2835 master mode driver
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * 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.
+ */
+
+#include <linux/clk.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/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
+#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_TIMEOUT (msecs_to_jiffies(1000))
+
+struct bcm2835_i2c_dev {
+	struct device *dev;
+	void __iomem *regs;
+	struct clk *clk;
+	int irq;
+	struct i2c_adapter adapter;
+	struct completion completion;
+	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);
+}
+
+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--;
+	}
+}
+
+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);
+	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, val);
+
+	err = val & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
+	if (err) {
+		i2c_dev->msg_err = err;
+		complete(&i2c_dev->completion);
+		return IRQ_HANDLED;
+	}
+
+	if (val & BCM2835_I2C_S_RXD) {
+		bcm2835_drain_rxfifo(i2c_dev);
+		if (!(val & BCM2835_I2C_S_DONE))
+			return IRQ_HANDLED;
+	}
+
+	if (val & BCM2835_I2C_S_DONE) {
+		if (i2c_dev->msg_buf_remaining)
+			i2c_dev->msg_err = BCM2835_I2C_S_LEN;
+		else
+			i2c_dev->msg_err = 0;
+		complete(&i2c_dev->completion);
+		return IRQ_HANDLED;
+	}
+
+	if (val & BCM2835_I2C_S_TXD) {
+		bcm2835_fill_txfifo(i2c_dev);
+		return IRQ_HANDLED;
+	}
+
+	return IRQ_NONE;
+}
+
+static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
+				struct i2c_msg *msg)
+{
+	u32 c;
+	int time_left;
+
+	i2c_dev->msg_buf = msg->buf;
+	i2c_dev->msg_buf_remaining = msg->len;
+	INIT_COMPLETION(i2c_dev->completion);
+
+	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
+
+	if (msg->flags & I2C_M_RD) {
+		c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
+	} else {
+		c = BCM2835_I2C_C_INTT;
+		bcm2835_fill_txfifo(i2c_dev);
+	}
+	c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD | BCM2835_I2C_C_I2CEN;
+
+	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);
+
+	time_left = wait_for_completion_timeout(&i2c_dev->completion,
+						BCM2835_I2C_TIMEOUT);
+	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
+	if (!time_left) {
+		dev_err(i2c_dev->dev, "i2c transfer timed out\n");
+		return -ETIMEDOUT;
+	}
+
+	if (likely(!i2c_dev->msg_err))
+		return 0;
+
+	if ((i2c_dev->msg_err & BCM2835_I2C_S_ERR) &&
+	    (msg->flags & I2C_M_IGNORE_NAK))
+		return 0;
+
+	dev_err(i2c_dev->dev, "i2c transfer failed: %x\n", i2c_dev->msg_err);
+
+	if (i2c_dev->msg_err & BCM2835_I2C_S_ERR)
+		return -EREMOTEIO;
+	else
+		return -EIO;
+}
+
+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);
+	int i;
+	int ret = 0;
+
+	for (i = 0; i < num; i++) {
+		ret = bcm2835_i2c_xfer_msg(i2c_dev, &msgs[i]);
+		if (ret)
+			break;
+	}
+
+	return ret ?: i;
+}
+
+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,
+};
+
+static int bcm2835_i2c_probe(struct platform_device *pdev)
+{
+	struct bcm2835_i2c_dev *i2c_dev;
+	struct resource *mem, *requested, *irq;
+	u32 bus_clk_rate, divider;
+	int ret;
+	struct i2c_adapter *adap;
+
+	i2c_dev = devm_kzalloc(&pdev->dev, sizeof(*i2c_dev), GFP_KERNEL);
+	if (!i2c_dev) {
+		dev_err(&pdev->dev, "Cannot allocate i2c_dev\n");
+		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);
+	if (!mem) {
+		dev_err(&pdev->dev, "No mem resource\n");
+		return -ENODEV;
+	}
+
+	requested = devm_request_mem_region(&pdev->dev, mem->start,
+					    resource_size(mem),
+					    dev_name(&pdev->dev));
+	if (!requested) {
+		dev_err(&pdev->dev, "Could not claim register region\n");
+		return -EBUSY;
+	}
+
+	i2c_dev->regs = devm_ioremap(&pdev->dev, mem->start,
+				     resource_size(mem));
+	if (!i2c_dev->regs) {
+		dev_err(&pdev->dev, "Could not map registers\n");
+		return -ENOMEM;
+	}
+
+	i2c_dev->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(i2c_dev->clk)) {
+		dev_err(&pdev->dev, "Could not get clock\n");
+		return PTR_ERR(i2c_dev->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 = 100000;
+	}
+
+	divider = DIV_ROUND_UP(clk_get_rate(i2c_dev->clk), bus_clk_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++;
+	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DIV, divider);
+
+	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_HWMON;
+	strlcpy(adap->name, "bcm2835 I2C adapter", sizeof(adap->name));
+	adap->algo = &bcm2835_i2c_algo;
+	adap->dev.parent = &pdev->dev;
+
+	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);
+
+	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,bcm2835-i2c" },
+	{},
+};
+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",
+		.owner	= THIS_MODULE,
+		.of_match_table = bcm2835_i2c_of_match,
+	},
+};
+module_platform_driver(bcm2835_i2c_driver);
+
+MODULE_AUTHOR("Stephen Warren <[e-mail]>");
+MODULE_DESCRIPTION("BCM2835 I2C bus adapter");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:i2c-bcm2835");