[i2c] [patch 4/8] I2C: S3C2410: Add a option of reducing the bus busy waiting time.

[Jean Delvare]

Hi Ben,

On Thu, 29 May 2008 14:22:48 +0100, Ben Dooks wrote:
> Add a single-master option to drasitcally reduce the time spent
> waiting to check the bus is free and ready for another transfer.

I don't understand. If you have a single-master bus, then the bus can
simply never be busy when you attempt to start a transaction. So, the
timeout setting shouldn't change anything, as you will get the bus
immediately anyway. Isn't it the case?

As a side note, this timeout loop is pretty broken anyway, as it
depends on the value of HZ. It should be adjusted to be time-based
rather than count-based.

> 
> Signed-off-by: Ben Dooks <ben-linux at fluff.org>
> 
> Index: linux-2.6.26-rc4-quilt2/drivers/i2c/busses/i2c-s3c2410.c
> ===================================================================
> --- linux-2.6.26-rc4-quilt2.orig/drivers/i2c/busses/i2c-s3c2410.c	2008-05-28 12:27:38.000000000 +0100
> +++ linux-2.6.26-rc4-quilt2/drivers/i2c/busses/i2c-s3c2410.c	2008-05-28 12:32:10.000000000 +0100
> @@ -472,8 +472,15 @@ static irqreturn_t s3c24xx_i2c_irq(int i
>  
>  static int s3c24xx_i2c_set_master(struct s3c24xx_i2c *i2c)
>  {
> +	struct s3c2410_platform_i2c *pdata;
>  	unsigned long iicstat;
> -	int timeout = 400;
> +	int timeout;
> +
> +	/* if we are a single master on this bus, reduce the delay awaiting
> +	 * for bus traffic to a much lower value. */
> +
> +	pdata = s3c24xx_i2c_get_platformdata(i2c->dev);
> +	timeout = (pdata->flags & S3C_IICFLG_SINGLE_MASTER) ? 10 : 400;
>  
>  	while (timeout-- > 0) {
>  		iicstat = readl(i2c->regs + S3C2410_IICSTAT);
> Index: linux-2.6.26-rc4-quilt2/include/asm-arm/plat-s3c/iic.h
> ===================================================================
> --- linux-2.6.26-rc4-quilt2.orig/include/asm-arm/plat-s3c/iic.h	2008-05-28 12:28:00.000000000 +0100
> +++ linux-2.6.26-rc4-quilt2/include/asm-arm/plat-s3c/iic.h	2008-05-28 12:32:10.000000000 +0100
> @@ -13,7 +13,8 @@
>  #ifndef __ASM_ARCH_IIC_H
>  #define __ASM_ARCH_IIC_H __FILE__
>  
> -#define S3C_IICFLG_FILTER	(1<<0)	/* enable s3c2440 filter */
> +#define S3C_IICFLG_FILTER	 (1<<0)	/* enable s3c2440 filter */
> +#define S3C_IICFLG_SINGLE_MASTER (1<<1) /* s3c24xx is only bus master. */
>  
>  /* Notes:
>   *	1) All frequencies are expressed in Hz
> 


-- 
Jean Delvare