[PATCH v2] drm/radeon/kms: Run DDC buses at 50 kbps

[Alex Deucher]

On Wed, Mar 21, 2012 at 9:30 AM, Jean Delvare <jdelvare at suse.de> wrote:
> A udelay value of 20 leads to an I2C bus running at only 25 kbps. I2C
> devices can typically operate faster than this, 50 kbps should be fine
> for all devices (and compliant devices can always stretch the clock if
> needed.)
>
> FWIW, the vast majority of framebuffer drivers set udelay to 10
> already. So set it to 10 in DRM drivers too, this will make EDID block
> reads faster. We might even lower the udelay value later if no problem
> is reported.

FWIW, our proprietary code uses 50 khz for i2c.  So I think it should be fine.

Alex

>
> Signed-off-by: Jean Delvare <jdelvare at suse.de>
> Reviewed-by: Alex Deucher <alexdeucher at gmail.com>
> Cc: Dave Airlie <airlied at gmail.com>
> ---
> Changes since v1:
> * Split per driver to make merging easier.
> * Make the subject line more accurate.
>
>  drivers/gpu/drm/radeon/radeon_i2c.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- linux-3.4-rc0.orig/drivers/gpu/drm/radeon/radeon_i2c.c      2012-03-21 13:43:33.753915151 +0100
> +++ linux-3.4-rc0/drivers/gpu/drm/radeon/radeon_i2c.c   2012-03-21 13:48:01.619472673 +0100
> @@ -925,7 +925,7 @@ struct radeon_i2c_chan *radeon_i2c_creat
>                i2c->algo.bit.setscl = set_clock;
>                i2c->algo.bit.getsda = get_data;
>                i2c->algo.bit.getscl = get_clock;
> -               i2c->algo.bit.udelay = 20;
> +               i2c->algo.bit.udelay = 10;
>                /* vesa says 2.2 ms is enough, 1 jiffy doesn't seem to always
>                 * make this, 2 jiffies is a lot more reliable */
>                i2c->algo.bit.timeout = 2;
>
> --
> Jean Delvare
> Suse L3