[i2c] [PATCH] Is review of AT91 patch pending?

[David Brownell]

> Personally, I would stick with the GPIO driver as it will work
> under all circumstances.

Yes; speaking of which, this is needed with current kernel GIT
on at91rm9200 platforms (now that i2c-at91 is marked BROKEN).
Something similar will be needed on at91sam926x systems too.

============= CUT HERE
Switch over to bitbanged GPIO for I2C.  The i2c-at91 controller
is fairly broken (gets underruns and overruns easily under load),
and its driver doesn't properly issue repeated START conditions
even in the handful of cases where the hardware supports them.
While the GPIO driver is slower, it doesn't have those issues.

Signed-off-by: David Brownell <dbrownell at users.sourceforge.net>
---
 arch/arm/mach-at91/at91rm9200_devices.c |   40 ++++++++++++++++----------------
 1 files changed, 20 insertions(+), 20 deletions(-)

--- a/arch/arm/mach-at91/at91rm9200_devices.c
+++ b/arch/arm/mach-at91/at91rm9200_devices.c
@@ -14,6 +14,7 @@
 #include <asm/mach/map.h>
 
 #include <linux/platform_device.h>
+#include <linux/i2c-gpio.h>
 
 #include <asm/arch/board.h>
 #include <asm/arch/gpio.h>
@@ -432,38 +433,37 @@ void __init at91_add_device_nand(struct 
 
 
 /* --------------------------------------------------------------------
- *  TWI (i2c)
+ *  TWI (i2c) ... use the GPIO code since this TWI controller is not
+ *  robust (gets overruns and underruns easily under slight loads)
+ *  and currently doesn't understand how to issue repeated STARTs.
  * -------------------------------------------------------------------- */
 
-#if defined(CONFIG_I2C_AT91) || defined(CONFIG_I2C_AT91_MODULE)
+#if defined(CONFIG_I2C_GPIO) || defined(CONFIG_I2C_GPIO_MODULE)
 
-static struct resource twi_resources[] = {
-	[0] = {
-		.start	= AT91RM9200_BASE_TWI,
-		.end	= AT91RM9200_BASE_TWI + SZ_16K - 1,
-		.flags	= IORESOURCE_MEM,
-	},
-	[1] = {
-		.start	= AT91RM9200_ID_TWI,
-		.end	= AT91RM9200_ID_TWI,
-		.flags	= IORESOURCE_IRQ,
-	},
+static struct i2c_gpio_platform_data pdata = {
+	.sda_pin		= AT91_PIN_PA25,
+	.sda_is_open_drain	= 1,
+	.scl_pin		= AT91_PIN_PA26,
+	.scl_is_open_drain	= 1,
+	.udelay			= 2,		/* ~100 KHz */
 };
 
 static struct platform_device at91rm9200_twi_device = {
-	.name		= "at91_i2c",
-	.id		= -1,
-	.resource	= twi_resources,
-	.num_resources	= ARRAY_SIZE(twi_resources),
+	.name			= "i2c-gpio",
+	.id			= -1,
+	.dev.platform_data	= &pdata,
 };
 
 void __init at91_add_device_i2c(void)
 {
-	/* pins used for TWI interface */
-	at91_set_A_periph(AT91_PIN_PA25, 0);		/* TWD */
+	/* pins used for TWI interface -- set as GPIO */
+
+	/* TWD: at91_set_A_periph(AT91_PIN_PA25, 0); */
+	at91_set_GPIO_periph(AT91_PIN_PA25, 1);
 	at91_set_multi_drive(AT91_PIN_PA25, 1);
 
-	at91_set_A_periph(AT91_PIN_PA26, 0);		/* TWCK */
+	/* TWCK: at91_set_A_periph(AT91_PIN_PA26, 0); */
+	at91_set_GPIO_periph(AT91_PIN_PA26, 1);
 	at91_set_multi_drive(AT91_PIN_PA26, 1);
 
 	platform_device_register(&at91rm9200_twi_device);