Re: [PATCH] drm/i915/dp: Validate cached link rate and lane count before retraining

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 27 Mar 2017, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Thu, Mar 23, 2017 at 04:11:32PM -0700, Manasi Navare wrote:
>> Currently intel_dp_check_link_status() tries to retrain the link if
>> Clock recovery or Channel EQ for any of the lanes indicated by
>> intel_dp->lane_count is not set. However these values cached in intel_dp
>> structure can be stale if link training has failed for these values
>> during previous modeset. Or these values can get stale since we have
>> now re read the DPCD registers or it can be 0 in case of connected boot
>> case.
>> 
>> This patch validates these values against the common_rates and max lane
>> count values.
>> 
>> This is absolutely required incase the common_rates or max lane count
>> are now different due to link fallback.
>> 
>> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
>> Cc: Jani Nikula <jani.nikula@linux.intel.com>
>> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 24 +++++++++++++++++++++---
>>  1 file changed, 21 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index fd96a6c..51fa6b5 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -295,6 +295,23 @@ static int intel_dp_link_rate_index(struct intel_dp *intel_dp,
>>  	return -1;
>>  }
>>  
>> +static bool intel_dp_link_params_is_valid(struct intel_dp *intel_dp)
>> +{
>> +	int common_rates[DP_MAX_SUPPORTED_RATES];
>> +	int link_rate_index;
>> +
>> +	link_rate_index = intel_dp_link_rate_index(intel_dp,
>> +						   common_rates,
>> +						   intel_dp->link_rate);
>
> Hmm. I thought we started to store the common rates somewhere more
> permanent, or did I imagine that?

That series got stalled waiting for Manasi's stuff to land... which
means it's now conflicting and pending rebase, and still waiting. :(

J.


>
>> +	if (link_rate_index < 0)
>> +		return false;
>> +	if (!intel_dp->lane_count ||
>> +	    (intel_dp->lane_count > intel_dp_max_lane_count(intel_dp)))
>
> Needless parens.
>
>> +		return false;
>> +
>> +	return true;
>> +}
>> +
>>  int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>>  					    int link_rate, uint8_t lane_count)
>>  {
>> @@ -4224,9 +4241,10 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>>  	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
>>  		return;
>>  
>> -	/* FIXME: we need to synchronize this sort of stuff with hardware
>> -	 * readout. Currently fast link training doesn't work on boot-up. */
>
> You shouldn't remove the FIXME. It's still totally valid.
>
>> -	if (!intel_dp->lane_count)
>> +	/* Validate the cached values of intel_dp->link_rate and
>> +	 * intel_dp->lane_count before attempting to retrain.
>> +	 */
>> +	if (!intel_dp_link_params_is_valid(intel_dp))
>>  		return;
>>  
>>  	/* Retrain if Channel EQ or CR not ok */
>> -- 
>> 2.1.4

-- 
Jani Nikula, Intel Open Source Technology Center
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