[PATCH] drm/dp: retry AUX transactions 32 times (v1.1)

[Jani Nikula]

On Wed, 26 Nov 2014, Dave Airlie <airlied at gmail.com> wrote:
> From: Dave Airlie <airlied at redhat.com>
>
> At least on two MST devices I've tested with, when
> they are link training downstream, they are totally
> unable to handle aux ch msgs, so they defer like nuts.
> I tried 16, it wasn't enough, 32 seems better.
>
> This fixes one Dell 4k monitor and one of the
> MST hubs.
>
> v1.1: fixup comment (Tom).

Missed this version, see my reply to v1:
http://mid.gmane.org/87k32iqppg.fsf@intel.com

Also, what if you avoid sink dpms off with:

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 70bb8d0b9695..768b1bfaea78 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1932,7 +1932,7 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
 
 	if (mode != DRM_MODE_DPMS_ON) {
 		ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
-					 DP_SET_POWER_D3);
+					 DP_SET_POWER_D0);
 	} else {
 		/*
 		 * When turning on, we need to retry for 1ms to give the sink

Does it make a difference?

BR,
Jani.


>
> Signed-off-by: Dave Airlie <airlied at redhat.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 959e207..79968e3 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -186,10 +186,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
>  
>  	/*
>  	 * The specification doesn't give any recommendation on how often to
> -	 * retry native transactions, so retry 7 times like for I2C-over-AUX
> -	 * transactions.
> +	 * retry native transactions. We used to retry 7 times like for
> +	 * aux i2c transactions but real world devices this wasn't
> +	 * sufficient, bump to 32 which makes Dell 4k monitors happier.
>  	 */
> -	for (retry = 0; retry < 7; retry++) {
> +	for (retry = 0; retry < 32; retry++) {
>  
>  		mutex_lock(&aux->hw_mutex);
>  		err = aux->transfer(aux, &msg);
> -- 
> 2.1.0
>
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-- 
Jani Nikula, Intel Open Source Technology Center