Re: [U-Boot] [PATCH 3/3] mpc5200: make i2c faster

[Sascha Hauer]

Hi,

On Sat, Mar 21, 2009 at 09:38:48AM -0400, Jon wrote:
> From: Sascha Hauer <s.ha...@pengutronix.de>
> 
> The mpc5xxx i2c driver has great delays while waiting for the chip status.
> make the delays smaller and the driver faster.
> 
> Signed-off-by: Sascha Hauer <s.ha...@pengutronix.de>
> ---
>  cpu/mpc5xxx/i2c.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/cpu/mpc5xxx/i2c.c b/cpu/mpc5xxx/i2c.c
> index 843af9c..41feb1d 100644
> --- a/cpu/mpc5xxx/i2c.c
> +++ b/cpu/mpc5xxx/i2c.c
> @@ -38,7 +38,7 @@ DECLARE_GLOBAL_DATA_PTR;
>  #error CONFIG_SYS_I2C_MODULE is not properly configured
>  #endif
>  
> -#define I2C_TIMEOUT  100
> +#define I2C_TIMEOUT  10000
>  #define I2C_RETRIES  3
>  
>  struct mpc5xxx_i2c_tap {
> @@ -94,7 +94,7 @@ static int wait_for_bb(void)
>               mpc_reg_out(&regs->mcr, 0, 0);
>               mpc_reg_out(&regs->mcr, I2C_EN, 0);
>  #endif
> -             udelay(1000);
> +             udelay(1);
>               status = mpc_reg_in(&regs->msr);
>       }
>  

The actual condition we wait for takes only a few useconds to become
true, but we wait for at least 1ms. As the I2C EEPROM environment
routine reads nearly the complete EEPROM several times during startup
the speed gain is enormous.
I can't recall if it was intentional to reduce the overall timeout with
this patch, but I can imagine that the i2c detect function will be
faster aswell.

> @@ -109,7 +109,7 @@ static int wait_for_pin(int *status)
>       *status = mpc_reg_in(&regs->msr);
>  
>       while (timeout-- && !(*status & I2C_IF)) {
> -             udelay(1000);
> +             udelay(1);
>               *status = mpc_reg_in(&regs->msr);

Same here.

Sascha

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