[Intel-gfx] [PATCH] drm/i915/ddi: Avoid long delays during system suspend / eDP disabling

[Jani Nikula]

On Thu, 01 Jun 2017, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
> On Thu, Jun 01, 2017 at 03:55:13PM +0300, Jani Nikula wrote:
>> On Wed, 31 May 2017, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
>> > On Wed, May 31, 2017 at 08:05:35PM +0300, Imre Deak wrote:
>> >> Atm disabling either DP or eDP outputs can generate a spurious short
>> >> pulse interrupt. The reason is that after disabling the port the source
>> >> will stop sending a valid stream data, while the sink expects either a
>> >> valid stream or the idle pattern. Since neither of this is sent the sink
>> >> assumes (after an arbitrary delay) that the link is lost and requests
>> >> for link retraining with a short pulse.
>> >> 
>> >> The spurious pulse is a real problem at least for eDP panels with long
>> >> power-off / power-cycle delays: as part of disabling the output we
>> >> disable the panel power. The subsequent spurious short pulse handling
>> >> will have to turn the power back on, which means the driver has to do a
>> >> redundant wait for the power-off and power-cycle delays. During system
>> >> suspend this leads to an unnecessary delay up to ~1s on systems with
>> >> such panels as reported by Rui.
>> >> 
>> >> To fix this put the sink to DPMS D3 state before turning off the port.
>> >> According to the DP spec in this state the sink should not request
>> >> retraining. This is also what we do already on pre-ddi platforms.
>> >> 
>> >> As an alternative I also tried configuring the port to send idle pattern
>> >> - which is against BSPec - and leave the port in normal mode before
>> >> turning off the port. Neither of these resolved the problem.
>> >> 
>> >> Cc: Zhang Rui <rui.zhang at intel.com>
>> >> Cc: David Weinehall <david.weinehall at linux.intel.com>
>> >> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> >> Reported-and-tested-by: Zhang Rui <rui.zhang at intel.com>
>> >> Signed-off-by: Imre Deak <imre.deak at intel.com>
>> >
>> > Makes sense to me.
>> 
>> I wonder if we should write D0 on hotplug.
>
> D0 is the default power state IIRC, so when you plug something in it
> should automagically go into D0. That's actually a slight problem
> power-wise if there's no subsequent modeset to drop it into D3.

Right. The thought was about branch devices that don't wake up and
aren't disconnected/reconnected after D3. But then we don't receive HPD
for them aither.

BR,
Jani.



-- 
Jani Nikula, Intel Open Source Technology Center