Re: [PATCH] drm/i915/dp: Don't stop the link when retraining

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

On Mon, 10 Nov 2014, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> On Mon,  3 Nov 2014 11:39:24 +0100
> Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
>> On pre-ddi platforms we don't shut down the link when changing link
>> training parameters. Except when clock recovery fails too hard and we
>> restart with channel eq training. Which doesn't make a lot of sense
>> really, since just stopping/restarting the DP port at this point
>> violates the modeset sequence documented in the Bspec.
>> 
>> So let's tempt fate and try this.
>> 
>> This patch is motivated by a WARN_ON triggered by
>> 
>> commit bc76e320f21f8bd790a72bd5dc06909617432352
>> Author: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Date:   Tue May 20 22:46:50 2014 +0200
>> 
>>     drm/i915: Drop now misleading DDI comment from dp_link_down
>> 
>> References: https://bugs.freedesktop.org/show_bug.cgi?id=85670
>> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 1 -
>>  1 file changed, 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c
>> b/drivers/gpu/drm/i915/intel_dp.c index f6a3fdd5589e..e48ca3a87199
>> 100644 --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -3598,7 +3598,6 @@ intel_dp_complete_link_train(struct intel_dp
>> *intel_dp) 
>>  		/* Try 5 times, then try clock recovery if that
>> fails */ if (tries > 5) {
>> -			intel_dp_link_down(intel_dp);
>>  			intel_dp_start_link_train(intel_dp);
>>  			intel_dp_set_link_train(intel_dp, &DP,
>>  						training_pattern |
>
>
> Didn't look like it helped the reporter?  Or at least I didn't see it
> tried in the bug above...

This wouldn't fix the bug, this would fix the backtrace from
WARN_ON(HAS_DDI(dev)) in intel_dp_link_down that's also present in the
bug. Just one more item in the long list of things that suck about our
DP link training.

BR,
Jani.


>
> I'm a bit worried about this because istr the spec indicating that we
> do need to down the link when retrying clock recovery.  I guess I'll
> need to check again.
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-- 
Jani Nikula, Intel Open Source Technology Center
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