Re: [PATCH 3/3] drm/i915/display: Increase number of fast wake precharge pulses

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Feb 21, 2024 at 09:53:22AM +0200, Jouni Högander wrote:
> Increasing number of fast wake sync pulses seem to fix problems with
> certain PSR panels. This should be ok for other panels as well as the eDP
> specification allows 10...16 precharge pulses and we are still within that
> range.

Hmm. Didn't we have some other panel that didn't like the original 16
precharge pulses? Or maybe that was just because we weren't using the
formula and thus we had a mismatch wrt. the fast wake stuff?

And are we sure this is definitely due to the precharge length
and not because eg. our idea of the io buffer on latency is too
short?

> 
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9739
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> index fad39b2e3022..4641c5bb8fb9 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -145,7 +145,7 @@ static int intel_dp_aux_sync_len(void)
>  
>  static u8 intel_dp_aux_fw_sync_len(void)
>  {
> -	u8 precharge = 10; /* 10-16 */
> +	u8 precharge = 12; /* 10-16 */

I think we need a comment to remind people why we are using a specific
value.

>  	u8 preamble = 8;
>  
>  	return precharge + preamble;
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel