[PATCH 2/2] drm/amd/display: Allow current eDP link settings to override verified ones.

[Mario Kleiner]

On Thu, Jan 9, 2020 at 7:44 PM Harry Wentland <hwentlan at amd.com> wrote:

> On 2020-01-09 10:20 a.m., Mario Kleiner wrote:
> > If the current eDP link settings, as read from hw, provide a higher
> > bandwidth than the verified_link_cap ones (= reported_link_cap), then
> > override verified_link_cap with current settings.
> >
> > These initial current eDP link settings have been set up by
> > firmware during boot, so they should work on the eDP panel.
> > Therefore use them if the firmware thinks they are good and
> > they provide higher link bandwidth, e.g., to enable higher
> > resolutions / color depths.
> >
>


Hi Harry, happy new year!

This only works when taking over from UEFI, so on boot or resume from
> hibernate. This wouldn't work on a normal suspend/resume.
>
>
See the other thread i just cc'ed you on. Depends if
dc_link_detect_helper() gets skipped/early returns or not on EDP. Some if
statement suggests it might get skipped on EDP + resume?


> Can you check if setting link->dc->config.optimize_edp_link_rate (see
> first if statement in detect_edp_sink_caps) fixes this? I imagine we
> need to read the reported settings from DP_SUPPORTED_LINK_RATES and fail
> to do so.
>

Tried that already (see other mail), replacing the whole if statement with
a if (true) to force reading DP_SUPPORTED_LINK_RATES. The whole table reads
back as all-zero, and versions are DP 1.1, eDP 1.3, not 1.4+ as what seems
to be required. The use the classic link bw stuff, but with a non-standard
link bandwidth multiplier of 0xc, and a reported DP_MAX_LINK_RATE of 0xa,
contradicting the 0xc setting that the firmware sets at bootup.

Seems to be a very Apple thing...
-mario


>
> Thanks,
> Harry
>
> > This fixes a problem found on the MacBookPro 2017 Retina panel:
> >
> > The panel reports 10 bpc color depth in its EDID, and the
> > firmware chooses link settings at boot which support enough
> > bandwidth for 10 bpc (324000 kbit/sec aka LINK_RATE_RBR2),
> > but the DP_MAX_LINK_RATE dpcd register only reports 2.7 Gbps
> > as possible, so verified_link_cap is only good for 2.7 Gbps
> > and 8 bpc, not providing the full color depth of the panel.
> >
> > Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
> > Cc: Alex Deucher <alexander.deucher at amd.com>
> > ---
> >  drivers/gpu/drm/amd/display/dc/core/dc_link.c | 21 +++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> > index 5ea4a1675259..f3acdb8fead5 100644
> > --- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> > +++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> > @@ -819,6 +819,27 @@ static bool dc_link_detect_helper(struct dc_link
> *link,
> >               case SIGNAL_TYPE_EDP: {
> >                       detect_edp_sink_caps(link);
> >                       read_current_link_settings_on_detect(link);
> > +
> > +                     /* If cur_link_settings provides higher bandwidth
> than
> > +                      * verified_link_cap, then use cur_link_settings
> as new
> > +                      * verified_link_cap, as it obviously works
> according to
> > +                      * firmware boot setup.
> > +                      *
> > +                      * This has been observed on the Apple MacBookPro
> 2017
> > +                      * Retina panel, which boots with a link setting
> higher
> > +                      * than what dpcd[DP_MAX_LINK_RATE] claims as
> possible.
> > +                      * Overriding allows to run the panel at 10 bpc /
> 30 bit.
> > +                      */
> > +                     if (dc_link_bandwidth_kbps(link,
> &link->cur_link_settings) >
> > +                         dc_link_bandwidth_kbps(link,
> &link->verified_link_cap)) {
> > +                             DC_LOG_DETECTION_DP_CAPS(
> > +                             "eDP current link setting bw %d kbps >
> verified_link_cap %d kbps. Override.",
> > +                             dc_link_bandwidth_kbps(link,
> &link->cur_link_settings),
> > +                             dc_link_bandwidth_kbps(link,
> &link->verified_link_cap));
> > +
> > +                             link->verified_link_cap =
> link->cur_link_settings;
> > +                     }
> > +
> >                       sink_caps.transaction_type =
> DDC_TRANSACTION_TYPE_I2C_OVER_AUX;
> >                       sink_caps.signal = SIGNAL_TYPE_EDP;
> >                       break;
> >
>
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