[Intel-gfx] [PATCH] drm/i915/dp: Link train Fallback on eDP only if fallback link BW can fit panel's native mode

[Wilson]

I believe this is the patch discussed here:

https://bugs.freedesktop.org/show_bug.cgi?id=105338

In which case....

Tested-By: Alexander Wilson

On 8/17/18 4:36 PM, Manasi Navare wrote:
> Thanks Lyude.
>
> So based on the imitial comments from Jani N, the recommendation was to disconnect
> downclock_mode from drrs_init so that user can set downclock mode
> independently from drrs mode.
>
> Jani,
> So we would need following changes:
> * Set the panel->downclock_mode in edp_init_connector() using intel_find_panel_downclock()
> * Add downclock_mode->clock when we check against available BW in mode_valid
> * Also use that in compute_config
> * Then check against downclock_mode on link training fallback
>
> Any more changes recommended here?
>
> Manasi
>
> On Fri, Aug 17, 2018 at 04:43:22PM -0400, Lyude Paul wrote:
>> On Fri, 2018-08-17 at 13:40 -0700, Manasi Navare wrote:
>>> On Fri, Aug 17, 2018 at 04:32:09PM -0400, Lyude Paul wrote:
>>>> After reading the discussion so far on this patch, this sounds correct! One
>>>> nit
>>>> pick below though:
>>>>
>>>> On Wed, 2018-05-16 at 19:21 -0700, Manasi Navare wrote:
>>>>> This patch fixes the original commit c0cfb10d9e1de49 ("drm/i915/edp:
>>>>> Do not do link training fallback or prune modes on EDP") that causes
>>>>> a blank screen in case of certain eDP panels (Eg: seen on Dell XPS13 9350)
>>>>> where first link training fails and a retraining is required by falling
>>>>> back to lower link rate/lane count.
>>>>> In case of some panels they advertise higher link rate/lane count
>>>>> than whats required for supporting the panel's native mode.
>>>>> But we always link train at highest link rate/lane count for eDP
>>>>> and if that fails we can still fallback to lower link rate/lane count
>>>>> as long as the fallback link BW still fits the native mode to avoid
>>>>> pruning the panel's native mode yet retraining at fallback values
>>>>> to recover from a blank screen.
>>>>>
>>>>> Cc: Clinton Taylor <clinton.a.taylor at intel.com>
>>>>> Cc: Jani Nikula <jani.nikula at linux.intel.com>
>>>>> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
>>>>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>>>>> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
>>>>> Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
>>>>> ---
>>>>>  drivers/gpu/drm/i915/intel_dp.c               | 25
>>>>> +++++++++++++++++++++++++
>>>>>  drivers/gpu/drm/i915/intel_dp_link_training.c | 26 +++++++++-------------
>>>>> ----
>>>>>  2 files changed, 34 insertions(+), 17 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/i915/intel_dp.c
>>>>> b/drivers/gpu/drm/i915/intel_dp.c
>>>>> index 2cc58596..7f7202a 100644
>>>>> --- a/drivers/gpu/drm/i915/intel_dp.c
>>>>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>>>>> @@ -387,6 +387,21 @@ static bool intel_dp_link_params_valid(struct
>>>>> intel_dp
>>>>> *intel_dp, int link_rate,
>>>>>  	return true;
>>>>>  }
>>>>>  
>>>>> +static bool intel_dp_can_link_train_fallback_for_edp(struct intel_dp
>>>>> *intel_dp,
>>>>> +						     int link_rate,
>>>>> +						     uint8_t lane_count)
>>>>> +{
>>>>> +	struct drm_display_mode *fixed_mode = intel_dp->attached_connector-
>>>>>> panel.fixed_mode;
>>>>> +	int mode_rate, max_rate;
>>>>> +
>>>>> +	mode_rate = intel_dp_link_required(fixed_mode->clock, 18);
>>>>> +	max_rate = intel_dp_max_data_rate(link_rate, lane_count);
>>>>> +	if (mode_rate > max_rate)
>>>>> +		return false;
>>>>> +
>>>>> +	return true;
>>>>> +}
>>>>> +
>>>>>  int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>>>>>  					    int link_rate, uint8_t lane_count)
>>>>>  {
>>>>> @@ -396,9 +411,19 @@ int intel_dp_get_link_train_fallback_values(struct
>>>>> intel_dp *intel_dp,
>>>>>  				    intel_dp->num_common_rates,
>>>>>  				    link_rate);
>>>>>  	if (index > 0) {
>>>>> +		if (intel_dp_is_edp(intel_dp) &&
>>>>> +		    !intel_dp_can_link_train_fallback_for_edp(intel_dp,
>>>>> +							     intel_dp-
>>>>>> common_rates[index-1],
>>>>> +							      lane_count))
>>>>> +			return -1;
>>>>>  		intel_dp->max_link_rate = intel_dp->common_rates[index - 1];
>>>>>  		intel_dp->max_link_lane_count = lane_count;
>>>>>  	} else if (lane_count > 1) {
>>>>> +		if (intel_dp_is_edp(intel_dp) &&
>>>>> +		    !intel_dp_can_link_train_fallback_for_edp(intel_dp,
>>>>> +							      intel_dp_max_commo
>>>>> n_rate(intel_dp),
>>>>> +							      lane_count >> 1))
>>>>> +			return -1;
>>>> The arguments you pass to intel_dp_can_link_train_fallback_for_edp() are the
>>>> same ones that you assign to intel_dp->max_link_rate and intel_dp-
>>>>> max_link_lane_count, why not just set those latter two first then pass
>>>>> them to
>>>> intel_dp_can_link_train_fallback_for_edp() afterwards?
>>> Actually I had thought of that. However if the
>>> intel_dp_can_link_train_fallback_for_edp()
>>> returns false then we dont wanna update the intel_dp->max_link_rate and
>>> lane_count to
>>> reduced fallback values.
>> Ahhh, that makes sense! Ignore that nitpick then :)
>>
>>> The other concerns mentioned on this patch were about checking them against
>>> downclock mode
>>> which will be with lower refresh rate hence might fit the reduced BW. But
>>> currently the
>>> downclock mode is assigned only as part of intel_dp_drrs_support() so first we
>>> would
>>> need to may be find that in edp_init and save it as part of intel_dp or
>>> something.
>>> As well as testing against alternate mode.
>>> Any thoughts on that?
>> That sounds fine to me! It is probably a bit safer then just blindly downgrading
>> the link
>>
>>> Manasi
>>>
>>>>>  		intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
>>>>>  		intel_dp->max_link_lane_count = lane_count >> 1;
>>>>>  	} else {
>>>>> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c
>>>>> b/drivers/gpu/drm/i915/intel_dp_link_training.c
>>>>> index 3fcaa98..6673975 100644
>>>>> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
>>>>> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
>>>>> @@ -335,22 +335,14 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
>>>>>  	return;
>>>>>  
>>>>>   failure_handling:
>>>>> -	/* Dont fallback and prune modes if its eDP */
>>>>> -	if (!intel_dp_is_edp(intel_dp)) {
>>>>> -		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link
>>>>> rate = %d, lane count = %d",
>>>>> -			      intel_connector->base.base.id,
>>>>> -			      intel_connector->base.name,
>>>>> -			      intel_dp->link_rate, intel_dp->lane_count);
>>>>> -		if (!intel_dp_get_link_train_fallback_values(intel_dp,
>>>>> -							     intel_dp-
>>>>>> link_rate,
>>>>> -							     intel_dp-
>>>>>> lane_count))
>>>>> -			/* Schedule a Hotplug Uevent to userspace to start
>>>>> modeset */
>>>>> -			schedule_work(&intel_connector->modeset_retry_work);
>>>>> -	} else {
>>>>> -		DRM_ERROR("[CONNECTOR:%d:%s] Link Training failed at link rate =
>>>>> %d, lane count = %d",
>>>>> -			  intel_connector->base.base.id,
>>>>> -			  intel_connector->base.name,
>>>>> -			  intel_dp->link_rate, intel_dp->lane_count);
>>>>> -	}
>>>>> +	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d,
>>>>> lane count = %d",
>>>>> +		      intel_connector->base.base.id,
>>>>> +		      intel_connector->base.name,
>>>>> +		      intel_dp->link_rate, intel_dp->lane_count);
>>>>> +	if (!intel_dp_get_link_train_fallback_values(intel_dp,
>>>>> +						     intel_dp->link_rate,
>>>>> +						     intel_dp->lane_count))
>>>>> +		/* Schedule a Hotplug Uevent to userspace to start modeset */
>>>>> +		schedule_work(&intel_connector->modeset_retry_work);
>>>>>  	return;
>>>>>  }
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