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

From: Mario Kleiner <mario.kleiner.de@gmail.com>
To: Alex Deucher <alexdeucher@gmail.com>,
	Harry Wentland <Harry.Wentland@amd.com>
Cc: mario.kleiner.de@gmail.de,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Maling list - DRI developers <dri-devel@lists.freedesktop.org>,
	Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: Re: [PATCH] drm/i915/dp: Add current maximum eDP link rate to sink_rate array.
Date: Thu, 9 Jan 2020 22:04:15 +0100	[thread overview]
Message-ID: <CAEsyxyjMsCU8rzyO0GewU_-uV5+UoDDwa5Mc74irUnJHhF6ALQ@mail.gmail.com> (raw)
In-Reply-To: <CADnq5_NPdg8MjQ5cB2aCD+US1Hv+FoP1gqKcA4W2e0pouG8cGQ@mail.gmail.com>

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On Thu, Jan 9, 2020 at 8:49 PM Alex Deucher <alexdeucher@gmail.com> wrote:

> On Thu, Jan 9, 2020 at 11:47 AM Mario Kleiner
> <mario.kleiner.de@gmail.com> wrote:
> >
> > On Thu, Jan 9, 2020 at 4:40 PM Alex Deucher <alexdeucher@gmail.com>
> wrote:
> >>
> >> On Thu, Jan 9, 2020 at 10:08 AM Mario Kleiner
> >> <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 <https://elixir.bootlin.com/linux/v5.5-rc5/ident/link>->connector_signal
== SIGNAL_TYPE_LVDS
<https://elixir.bootlin.com/linux/v5.5-rc5/ident/SIGNAL_TYPE_LVDS> ||
			link <https://elixir.bootlin.com/linux/v5.5-rc5/ident/link>->connector_signal
== SIGNAL_TYPE_EDP
<https://elixir.bootlin.com/linux/v5.5-rc5/ident/SIGNAL_TYPE_EDP>) &&
			link <https://elixir.bootlin.com/linux/v5.5-rc5/ident/link>->local_sink)
		return <https://elixir.bootlin.com/linux/v5.5-rc5/ident/return> true
<https://elixir.bootlin.com/linux/v5.5-rc5/ident/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...

-mario

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