Re: [PATCH v3 2/2] i2c: Davinci i2c bus recovery procedure to clear the bus

[Ben Dooks <ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org>]

On Tue, Jan 12, 2010 at 04:47:16PM +0530, Philby John wrote:
> >From 2565eeda807e49376298ec895a0d9a91a7668417 Mon Sep 17 00:00:00 2001
> From: Philby John <pjohn-k0rHJ+Hhz/SB+jHODAdFcQ@public.gmane.org>
> Date: Mon, 11 Jan 2010 22:39:44 +0530
> Subject: [PATCH 2/2] Davinci i2c bus recovery procedure to clear the bus
> 
> Come out of i2c time out condition by following the
> bus recovery procedure outlined in the i2c protocol v3 spec.
> The kernel must be robust enough to gracefully recover
> from i2c bus failure without having to reset the machine.
> This is done by first NACKing the slave, pulsing the SCL
> line 9 times and then sending the stop command.
> 
> This patch has been tested on a DM6446 and DM355

Still not sure whether this can be included as a bug-fix or whether
it comes under the new feature category. Also, since it has to get
new data from the platform whose tree it should really go into.
 
> Signed-off-by: Philby John <pjohn-k0rHJ+Hhz/SB+jHODAdFcQ@public.gmane.org>
> Signed-off-by: Srinivasan, Nageswari <nageswari-l0cyMroinI0@public.gmane.org>
> ---
>  drivers/i2c/busses/i2c-davinci.c |   57 +++++++++++++++++++++++++++++++++++--
>  1 files changed, 53 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
> index 35f9daa..5459065 100644
> --- a/drivers/i2c/busses/i2c-davinci.c
> +++ b/drivers/i2c/busses/i2c-davinci.c
> @@ -36,6 +36,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/io.h>
>  #include <linux/cpufreq.h>
> +#include <linux/gpio.h>
>  
>  #include <mach/hardware.h>
>  #include <mach/i2c.h>
> @@ -43,6 +44,7 @@
>  /* ----- global defines ----------------------------------------------- */
>  
>  #define DAVINCI_I2C_TIMEOUT	(1*HZ)
> +#define DAVINCI_I2C_MAX_TRIES	2
>  #define I2C_DAVINCI_INTR_ALL    (DAVINCI_I2C_IMR_AAS | \
>  				 DAVINCI_I2C_IMR_SCD | \
>  				 DAVINCI_I2C_IMR_ARDY | \
> @@ -130,6 +132,44 @@ static inline u16 davinci_i2c_read_reg(struct davinci_i2c_dev *i2c_dev, int reg)
>  	return __raw_readw(i2c_dev->base + reg);
>  }
>  
> +/* Generate a pulse on the i2c clock pin. */
> +static void generic_i2c_clock_pulse(unsigned int scl_pin)
> +{
> +	u16 i;
> +
> +	if (scl_pin) {
> +		/* Send high and low on the SCL line */
> +		for (i = 0; i < 9; i++) {
> +			gpio_set_value(scl_pin, 0);
> +			udelay(20);
> +			gpio_set_value(scl_pin, 1);
> +			udelay(20);
> +		}
> +	}
> +}
> +
> +/* This routine does i2c bus recovery as specified in the
> + * i2c protocol Rev. 03 section 3.16 titled "Bus clear"
> + */
> +static void i2c_recover_bus(struct davinci_i2c_dev *dev)
> +{
> +	u32 flag = 0;
> +	struct davinci_i2c_platform_data *pdata = dev->dev->platform_data;
> +
> +	dev_err(dev->dev, "initiating i2c bus recovery\n");
> +	/* Send NACK to the slave */
> +	flag = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG);
> +	flag |=  DAVINCI_I2C_MDR_NACK;
> +	/* write the data into mode register */
> +	davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, flag);
> +	if (pdata)
> +		generic_i2c_clock_pulse(pdata->scl_pin);
> +	/* Send STOP */
> +	flag = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG);
> +	flag |= DAVINCI_I2C_MDR_STP;
> +	davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, flag);
> +}
> +
>  static inline void davinci_i2c_reset_ctrl(struct davinci_i2c_dev *i2c_dev,
>  								int val)
>  {
> @@ -235,14 +275,22 @@ static int i2c_davinci_wait_bus_not_busy(struct davinci_i2c_dev *dev,
>  					 char allow_sleep)
>  {
>  	unsigned long timeout;
> +	static u16 to_cnt;
>  
>  	timeout = jiffies + dev->adapter.timeout;
>  	while (davinci_i2c_read_reg(dev, DAVINCI_I2C_STR_REG)
>  	       & DAVINCI_I2C_STR_BB) {
> -		if (time_after(jiffies, timeout)) {
> -			dev_warn(dev->dev,
> -				 "timeout waiting for bus ready\n");
> -			return -ETIMEDOUT;
> +		if (to_cnt <= DAVINCI_I2C_MAX_TRIES) {
> +			if (time_after(jiffies, timeout)) {
> +				dev_warn(dev->dev,
> +				"timeout waiting for bus ready\n");
> +				to_cnt++;
> +				return -ETIMEDOUT;
> +			} else {
> +				to_cnt = 0;
> +				i2c_recover_bus(dev);
> +				i2c_davinci_init(dev);
> +			}
>  		}
>  		if (allow_sleep)
>  			schedule_timeout(1);
> @@ -324,6 +372,7 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
>  						      dev->adapter.timeout);
>  	if (r == 0) {
>  		dev_err(dev->dev, "controller timed out\n");
> +		i2c_recover_bus(dev);
>  		i2c_davinci_init(dev);
>  		dev->buf_len = 0;
>  		return -ETIMEDOUT;
> -- 
> 1.6.3.3.MVISTA
> 
> 
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-i2c" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Ben (ben-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'