Re: [Intel-gfx] [PATCH] drm/i915/dp: Add current maximum eDP link rate to sink_rate array.

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Harry Wentland <hwentlan@amd.com>
Cc: mario.kleiner.de@gmail.de, Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Maling list - DRI developers <dri-devel@lists.freedesktop.org>
Subject: Re: [Intel-gfx] [PATCH] drm/i915/dp: Add current maximum eDP link rate to sink_rate array.
Date: Fri, 10 Jan 2020 20:09:44 +0200	[thread overview]
Message-ID: <20200110180944.GL13686@intel.com> (raw)
In-Reply-To: <bae132f3-73e6-5004-c9a9-adb632338268@amd.com>

On Thu, Jan 09, 2020 at 04:26:19PM -0500, Harry Wentland wrote:
> 
> 
> On 2020-01-09 4:04 p.m., Mario Kleiner wrote:
> > On Thu, Jan 9, 2020 at 8:49 PM Alex Deucher <alexdeucher@gmail.com
> > <mailto:alexdeucher@gmail.com>> wrote:
> >
> >     On Thu, Jan 9, 2020 at 11:47 AM Mario Kleiner
> >     <mario.kleiner.de@gmail.com <mailto:mario.kleiner.de@gmail.com>>
> >     wrote:
> >     >
> >     > On Thu, Jan 9, 2020 at 4:40 PM Alex Deucher
> >     <alexdeucher@gmail.com <mailto:alexdeucher@gmail.com>> wrote:
> >     >>
> >     >> On Thu, Jan 9, 2020 at 10:08 AM Mario Kleiner
> >     >> <mario.kleiner.de@gmail.com
> >     <mailto:mario.kleiner.de@gmail.com>> wrote:
> >     >> >
> >     As Harry mentioned in the other thread, won't this only work if the
> >     display was brought up by the vbios?  In the suspend/resume case,
> >     won't we just fall back to 2.7Gbps?
> >
> >     Alex
> >
> >
> > Adding Harry to cc...
> >
> > The code is only executed for eDP. On the Intel side, it seems that
> > intel_edp_init_dpcd() gets only called during driver load /
> > modesetting init, so not on resume.
> >
> > On the AMD DC side, dc_link_detect_helper() has this early no-op
> > return at the beginning:
> >
> > if ((link->connector_signal == SIGNAL_TYPE_LVDS ||
> > 			link->connector_signal == SIGNAL_TYPE_EDP) &&
> > 			link->local_sink)
> > 		return true;
> >
> > So i guess if link->local_sink doesn't get NULL'ed during a
> > suspend/resume cycle, then we never reach the setup code that would
> > overwrite with non vbios settings?
> >
> > Sounds reasonable to me, given that eDP panels are usually fixed
> > internal panels, nothing that gets hot(un-)plugged?
> >
> > I can't test, because suspend/resume with the Polaris gpu on the MBP
> > 2017 is totally broken atm., just as vgaswitcheroo can't do its job.
> > Looks like powering down the gpu works, but powering up doesn't. And
> > also modesetting at vgaswitcheroo switch time is no-go, because the
> > DDC/AUX lines apparently can't be switched on that Apple gmux, and
> > handover of that data seems to be not implemented in current
> > vgaswitcheroo. At the moment switching between AMD only or Intel+AMD
> > Prime setup is quite a pita...
> >
> 
> I haven't followed the entire discussion on the i915 thread but for the
> amdgpu dc patch I would prefer a DPCD quirk to override the reported
> link settings with the correct link rate.

We could consider adding a standard function for reading the receiver
caps and applying the quirk there. I have a feeling that putting it
into drm_dp_dpcd_read() would be a bit too low level since it would
prevent reading the non-quirked raw data easily.

-- 
Ville Syrjälä
Intel
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