Re: [PATCH v5 5/5] drm/i915/display: Increase number of fast wake precharge pulses

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: "Jouni Högander" <jouni.hogander@intel.com>
Cc: intel-gfx@lists.freedesktop.org,
	Jani Nikula <jani.nikula@linux.intel.com>
Subject: Re: [PATCH v5 5/5] drm/i915/display: Increase number of fast wake precharge pulses
Date: Tue, 12 Mar 2024 18:44:42 +0200	[thread overview]
Message-ID: <ZfCGekSEs_gS9zUZ@intel.com> (raw)
In-Reply-To: <20240308110039.3900838-6-jouni.hogander@intel.com>

On Fri, Mar 08, 2024 at 01:00:39PM +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.
> 
> 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 7e69be100d90..5dff1bc85d61 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)
>  
>  int intel_dp_aux_fw_sync_len(void)
>  {
> -	int precharge = 10; /* 10-16 */
> +	int precharge = 12; /* 10-16 */

This is still giving me allergies because Windows doesn't have
anything like this. So the mystery is how does Windows work?
This was an actual production machine I take it?

Did we have look at the error bits in PSR2_DEBUG to see if there
is some difference between the working and non-working values?

Anyways, this at least needs a proper comment to explain why
we're not usign the standard value.

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

-- 
Ville Syrjälä
Intel