[PATCH V3 2/4] drivers/i2c/busses/i2c-at91.c: add new driver

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This driver has the following properties compared to the old driver:
1. Support for multiple interfaces.
2. Interrupt driven I/O as opposed to polling/busy waiting.
3. Support for _one_ repeated start (Sr) condition, which is enough
   for most real-world applications including all SMBus transfer types.
   (The hardware does not support issuing arbitrary Sr conditions on the
    bus.)

Tested on Atmel G45 with BQ20Z80 battery SMBus client.

Signed-off-by: Nikolaus Voss <n.voss@xxxxxxxxxxx>
---
 drivers/i2c/busses/Kconfig    |   11 +-
 drivers/i2c/busses/i2c-at91.c |  442 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 446 insertions(+), 7 deletions(-)
 create mode 100644 drivers/i2c/busses/i2c-at91.c

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 646068e..c4b6bdc 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -286,18 +286,15 @@ comment "I2C system bus drivers (mostly embedded / system-on-chip)"
 
 config I2C_AT91
 	tristate "Atmel AT91 I2C Two-Wire interface (TWI)"
-	depends on ARCH_AT91 && EXPERIMENTAL && BROKEN
+	depends on ARCH_AT91 && EXPERIMENTAL
 	help
 	  This supports the use of the I2C interface on Atmel AT91
 	  processors.
 
-	  This driver is BROKEN because the controller which it uses
-	  will easily trigger RX overrun and TX underrun errors.  Using
-	  low I2C clock rates may partially work around those issues
-	  on some systems.  Another serious problem is that there is no
-	  documented way to issue repeated START conditions, as needed
+	  A serious problem is that there is no documented way to issue
+	  repeated START conditions for more than two messages, as needed
 	  to support combined I2C messages.  Use the i2c-gpio driver
-	  unless your system can cope with those limitations.
+	  unless your system can cope with this limitation.
 
 config I2C_AU1550
 	tristate "Au1550/Au1200 SMBus interface"
diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
new file mode 100644
index 0000000..e35479b
--- /dev/null
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -0,0 +1,442 @@
+/*
+
+    i2c Support for Atmel's AT91 Two-Wire Interface (TWI)
+
+    Copyright (C) 2011 Nikolaus Voss <n.voss@xxxxxxxxxxx>
+
+    Evolved from original work by:
+    Copyright (C) 2004 Rick Bronson
+    Converted to 2.6 by Andrew Victor <andrew@xxxxxxxxxxxxx>
+
+    Borrowed heavily from original work by:
+    Copyright (C) 2000 Philip Edelbrock <phil@xxxxxxxxxxxxxxxxxxxx>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+*/
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/clk.h>
+#include <linux/platform_device.h>
+#include <linux/io.h>
+
+#include <mach/at91_twi.h>
+#include <mach/board.h>
+#include <mach/cpu.h>
+
+#define TWI_CLOCK		100000		/* Hz. max 400 Kbits/sec */
+#define AT91_I2C_TIMEOUT	(HZ/100)	/* transfer timeout */
+
+struct at91_twi_dev {
+	struct device *dev;
+	void __iomem *base;
+	struct completion cmd_complete;
+	struct clk *clk;
+	u8 *buf;
+	size_t buf_len;
+	int irq;
+	unsigned transfer_status;
+	struct i2c_adapter adapter;
+};
+
+static inline unsigned at91_twi_read(struct at91_twi_dev *dev, unsigned reg)
+{
+	return __raw_readl(dev->base + (reg));
+}
+
+static inline void at91_twi_write(struct at91_twi_dev *dev, unsigned reg,
+				  unsigned val)
+{
+	__raw_writel((val), dev->base + (reg));
+}
+
+static inline void at91_disable_twi_interrupts(struct at91_twi_dev *dev)
+{
+	at91_twi_write(dev, AT91_TWI_IDR,
+		       AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY);
+}
+
+static void at91_init_twi_bus(struct at91_twi_dev *dev)
+{
+	at91_disable_twi_interrupts(dev);
+	at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SWRST);
+	at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_MSEN);
+	at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SVDIS);
+}
+
+static void at91_set_twi_clock(struct at91_twi_dev *dev)
+{
+	unsigned long cdiv, ckdiv;
+
+	/* Calcuate clock dividers */
+	cdiv = (clk_get_rate(dev->clk) / (2 * TWI_CLOCK)) - 3;
+	cdiv = cdiv + 1;	/* round up */
+	ckdiv = 0;
+	while (cdiv > 255) {
+		ckdiv++;
+		cdiv = cdiv >> 1;
+	}
+
+	if (cpu_is_at91rm9200()) {			/* AT91RM9200 Errata #22 */
+		if (ckdiv > 5) {
+			printk(KERN_ERR "AT91 I2C: Invalid TWI_CLOCK value!\n");
+			ckdiv = 5;
+		}
+	}
+
+	at91_twi_write(dev, AT91_TWI_CWGR, (ckdiv << 16) | (cdiv << 8) | cdiv);
+}
+
+static void __devinit at91_twi_hwinit(struct at91_twi_dev *dev)
+{
+	at91_init_twi_bus(dev);
+	at91_set_twi_clock(dev);
+}
+
+static void at91_twi_write_next_byte(struct at91_twi_dev *dev)
+{
+	if (dev->buf_len > 0) {
+
+		const u8 c = *(dev->buf++);
+
+		at91_twi_write(dev, AT91_TWI_THR, c);
+
+		/* send stop when last byte has been written */
+		if (--dev->buf_len == 0)
+			at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
+
+		dev_dbg(dev->dev, "wrote 0x%x, to go %d\n", c, dev->buf_len);
+	}
+}
+
+static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
+{
+	const u8 c = at91_twi_read(dev, AT91_TWI_RHR) & 0xff;
+
+	*(dev->buf)++ = c;
+
+	/* send stop if second but last byte has been read */
+	if (--dev->buf_len == 1)
+		at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
+
+	dev_dbg(dev->dev, "read 0x%x, to go %d\n", c, dev->buf_len);
+}
+
+static irqreturn_t atmel_twi_interrupt(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);
+
+	if (irqstatus & AT91_TWI_TXCOMP) {
+		at91_disable_twi_interrupts(dev);
+		dev->transfer_status = status;
+		complete(&dev->cmd_complete);
+	}
+	else if (irqstatus & AT91_TWI_RXRDY) {
+		at91_twi_read_next_byte(dev);
+	}
+	else if (irqstatus & AT91_TWI_TXRDY) {
+		at91_twi_write_next_byte(dev);
+	}
+	else {
+		return IRQ_NONE;
+	}
+
+	return IRQ_HANDLED;
+}
+
+int at91_do_twi_transfer(struct at91_twi_dev *dev, bool is_read)
+{
+	int ret = 0;
+
+	INIT_COMPLETION(dev->cmd_complete);
+
+	if (is_read) {
+		if (!dev->buf_len)
+			at91_twi_write(dev, AT91_TWI_CR,
+				       AT91_TWI_START | AT91_TWI_STOP);
+		else
+			at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_START);
+
+		at91_twi_write(dev, AT91_TWI_IER,
+			       AT91_TWI_TXCOMP | AT91_TWI_RXRDY);
+
+	} else {
+
+		at91_twi_write_next_byte(dev);
+
+		at91_twi_write(dev, AT91_TWI_IER,
+			       AT91_TWI_TXCOMP | AT91_TWI_TXRDY);
+	}
+
+	ret = wait_for_completion_interruptible_timeout(&dev->cmd_complete,
+							dev->adapter.timeout);
+	if (ret == 0) {
+		dev_err(dev->dev, "controller timed out\n");
+		at91_init_twi_bus(dev);
+		return -ETIMEDOUT;
+	}
+
+	if (dev->transfer_status & AT91_TWI_NACK) {
+		dev_dbg(dev->dev, "received nack\n");
+		return -ENODEV;
+	}
+
+	if (dev->transfer_status & AT91_TWI_OVRE) {
+		dev_err(dev->dev, "overrun while reading\n");
+		return -EIO;
+	}
+
+	dev_dbg(dev->dev, "transfer complete\n");
+
+	return 0;
+}
+
+static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
+{
+	struct at91_twi_dev *dev = i2c_get_adapdata(adap);
+	int ret;
+	unsigned int_addr_flag = 0;
+	struct i2c_msg *m_start = msg;
+
+	dev_dbg(&adap->dev, "at91_xfer: processing %d messages:\n", num);
+
+	/* the hardware can handle at most two messages concatenated by a
+	 * repeated start via it's internal address feature.
+	 */
+	if (num > 2) {
+		dev_err(dev->dev,
+			"cannot handle more than two concatenated messages.\n");
+		return 0;
+
+	} else if (num == 2) {
+
+		int internal_address = 0;
+		int i;
+
+		if (msg->flags & I2C_M_RD) {
+			dev_err(dev->dev, "first transfer must be write.\n");
+			return 0;
+		}
+
+		if (msg->len > 3) {
+			dev_err(dev->dev, "first message size must be <= 3.\n");
+			return 0;
+		}
+
+		/* 1st msg is put into the internal address, start with 2nd */
+		m_start = &msg[1];
+
+		for (i = 0; i < msg->len; ++i) {
+			internal_address |= ((unsigned)msg->buf[i]) << (8 * i);
+			int_addr_flag += AT91_TWI_IADRSZ_1;
+		}
+
+		at91_twi_write(dev, AT91_TWI_IADR, internal_address);
+	}
+
+	at91_twi_write(dev, AT91_TWI_MMR, (m_start->addr << 16) | int_addr_flag
+		       | ((m_start->flags & I2C_M_RD) ? AT91_TWI_MREAD : 0));
+
+	dev->buf_len = m_start->len;
+	dev->buf = m_start->buf;
+
+	ret = at91_do_twi_transfer(dev, m_start->flags & I2C_M_RD);
+
+	if (ret < 0)
+		return ret;
+
+	return num;
+}
+
+static u32 at91_twi_func(struct i2c_adapter *adapter)
+{
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
+}
+
+static struct i2c_algorithm at91_twi_algorithm = {
+	.master_xfer	= at91_twi_xfer,
+	.functionality	= at91_twi_func,
+};
+
+static int __devinit at91_twi_probe(struct platform_device *pdev)
+{
+	struct at91_twi_dev *dev;
+	struct resource *mem, *irq, *ioarea;
+	int rc;
+
+	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!mem)
+		return -ENODEV;
+
+	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
+	if (!irq)
+		return -ENODEV;
+
+	ioarea = request_mem_region(mem->start, resource_size(mem), pdev->name);
+	if (!ioarea)
+		return -EBUSY;
+
+	dev = kzalloc(sizeof(struct at91_twi_dev), GFP_KERNEL);
+	if (!dev) {
+		rc = -ENOMEM;
+		goto err_release_region;
+	}
+
+	init_completion(&dev->cmd_complete);
+
+	dev->dev = get_device(&pdev->dev);
+	dev->irq = irq->start;
+	platform_set_drvdata(pdev, dev);
+
+	dev->clk = clk_get(&pdev->dev, "twi_clk");
+	if (IS_ERR(dev->clk)) {
+		dev_err(&pdev->dev, "no clock defined\n");
+		rc = -ENODEV;
+		goto err_free_mem;
+	}
+	clk_enable(dev->clk);
+
+	dev->base = ioremap(mem->start, resource_size(mem));
+	if (!dev->base) {
+		rc = -EBUSY;
+		goto err_mem_ioremap;
+	}
+
+	at91_twi_hwinit(dev);
+
+	rc = request_irq(dev->irq, atmel_twi_interrupt, 0,
+			 dev_name(&pdev->dev), dev);
+	if (rc) {
+		dev_err(&pdev->dev, "Cannot get irq %d: %d\n", dev->irq, rc);
+		goto err_unuse_clocks;
+	}
+
+	snprintf(dev->adapter.name, sizeof(dev->adapter.name), "AT91");
+	i2c_set_adapdata(&dev->adapter, dev);
+	dev->adapter.owner = THIS_MODULE;
+	dev->adapter.class = I2C_CLASS_HWMON;
+	dev->adapter.algo = &at91_twi_algorithm;
+	dev->adapter.dev.parent = &pdev->dev;
+	dev->adapter.nr = pdev->id;
+	dev->adapter.timeout = AT91_I2C_TIMEOUT;
+
+	rc = i2c_add_numbered_adapter(&dev->adapter);
+	if (rc) {
+		dev_err(&pdev->dev, "Adapter %s registration failed\n",
+			dev->adapter.name);
+		goto err_free_irq;
+	}
+
+	dev_info(&pdev->dev, "AT91 i2c bus driver.\n");
+	return 0;
+
+err_free_irq:
+	free_irq(dev->irq, dev);
+err_unuse_clocks:
+	iounmap(dev->base);
+err_mem_ioremap:
+	clk_disable(dev->clk);
+	clk_put(dev->clk);
+	dev->clk = NULL;
+err_free_mem:
+	platform_set_drvdata(pdev, NULL);
+	put_device(&pdev->dev);
+	kfree(dev);
+err_release_region:
+	release_mem_region(mem->start, resource_size(mem));
+
+	return rc;
+}
+
+static int __devexit at91_twi_remove(struct platform_device *pdev)
+{
+	struct at91_twi_dev *dev = platform_get_drvdata(pdev);
+	struct resource *mem;
+	int rc;
+
+	platform_set_drvdata(pdev, NULL);
+	rc = i2c_del_adapter(&dev->adapter);
+	put_device(&pdev->dev);
+
+	clk_disable(dev->clk);
+	clk_put(dev->clk);
+	dev->clk = NULL;
+
+	free_irq(dev->irq, dev);
+
+	iounmap(dev->base);
+	kfree(dev);
+
+	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	release_mem_region(mem->start, resource_size(mem));
+
+	return rc;
+}
+
+#ifdef CONFIG_PM
+
+static int at91_twi_suspend(struct device *dev)
+{
+	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
+
+	clk_disable(twi_dev->clk);
+
+	return 0;
+}
+
+static int at91_twi_resume(struct device *dev)
+{
+	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
+
+	return clk_enable(twi_dev->clk);
+}
+
+static const struct dev_pm_ops at91_twi_pm = {
+	.suspend	= at91_twi_suspend,
+	.resume		= at91_twi_resume,
+};
+
+#define at91_twi_pm_ops (&at91_twi_pm)
+#else
+#define at91_twi_pm_ops NULL
+#endif
+
+MODULE_ALIAS("platform:at91_i2c");
+
+static struct platform_driver at91_twi_driver = {
+	.probe		= at91_twi_probe,
+	.remove		= __devexit_p(at91_twi_remove),
+	.driver		= {
+		.name	= "at91_i2c",
+		.owner	= THIS_MODULE,
+		.pm	= at91_twi_pm_ops,
+	},
+};
+
+static int __init at91_twi_init(void)
+{
+	return platform_driver_register(&at91_twi_driver);
+}
+
+static void __exit at91_twi_exit(void)
+{
+	platform_driver_unregister(&at91_twi_driver);
+}
+
+module_init(at91_twi_init);
+module_exit(at91_twi_exit);
+
+MODULE_AUTHOR("Nikolaus Voss");
+MODULE_DESCRIPTION("I2C (TWI) driver for Atmel AT91");
+MODULE_LICENSE("GPL");
-- 
1.7.5.4

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