[PATCH 1/2] drm/kms: Make i2c buses faster

[Alex Deucher]

On Sat, Jan 28, 2012 at 5:07 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.
>
> Signed-off-by: Jean Delvare <jdelvare at suse.de>
> Acked-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: Keith Packard <keithp at keithp.com>
> Cc: Alex Deucher <alexdeucher at gmail.com>

Reviewed-by: Alex Deucher <alexdeucher at gmail.com>

> ---
> Already sent on: 2011-10-21.
>
>  drivers/gpu/drm/i915/intel_i2c.c    |    2 +-
>  drivers/gpu/drm/radeon/radeon_i2c.c |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> --- linux-3.3-rc1.orig/drivers/gpu/drm/i915/intel_i2c.c 2012-01-28 10:12:16.554480007 +0100
> +++ linux-3.3-rc1/drivers/gpu/drm/i915/intel_i2c.c      2012-01-28 10:28:16.884668894 +0100
> @@ -37,7 +37,7 @@
>
>  /* Intel GPIO access functions */
>
> -#define I2C_RISEFALL_TIME 20
> +#define I2C_RISEFALL_TIME 10
>
>  static inline struct intel_gmbus *
>  to_intel_gmbus(struct i2c_adapter *i2c)
> --- linux-3.3-rc1.orig/drivers/gpu/drm/radeon/radeon_i2c.c      2012-01-28 10:12:16.555480007 +0100
> +++ linux-3.3-rc1/drivers/gpu/drm/radeon/radeon_i2c.c   2012-01-28 10:28:16.886668894 +0100
> @@ -924,7 +924,7 @@ 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