On Thu, Jan 09, 2020 at 05:30:05PM +0100, Mario Kleiner wrote:
> On Thu, Jan 9, 2020 at 4:38 PM Ville Syrjälä <ville.syrjala@linux.intel.com>
> wrote:
>
> > On Thu, Jan 09, 2020 at 05:26:57PM +0200, Ville Syrjälä wrote:
> > > On Thu, Jan 09, 2020 at 04:07:52PM +0100, Mario Kleiner wrote:
> > > > The panel reports 10 bpc color depth in its EDID, and the UEFI
> > > > firmware chooses link settings at boot which support enough
> > > > bandwidth for 10 bpc (324000 kbit/sec to be precise), but the
> > > > DP_MAX_LINK_RATE dpcd register only reports 2.7 Gbps as possible,
> >
> > Does it actually or do we just ignore the fact that it reports 3.24Gbps?
> >
> > If it really reports 3.24 then we should be able to just add that to
> > dp_rates[] in intel_dp_set_sink_rates() and be done with it.
> >
> > Although we'd likely want to skip 3.24 unless it really is reported
> > as the max so as to not use that non-standard rate on other displays.
> > So would require a bit fancier logic for that.
> >
> >
> Was also my initial thought, but the DP_MAX_LINK_RATE reg reports 2.7 Gbps
> as maximum.
So dpcd[0x1] == 0xa ?
Yes. [*]
What about the magic second version of DP_MAX_LINK_RATE at 0x2201 ?
Hmm. I guess we should already be reading that via
intel_dp_extended_receiver_capabilities().
Yes, you do.
[*] Well, i have to recheck on the machine. I started this work on the AMD side and checked what AMD DC gave me, haven't rechecked stuff under i915 that i already knew from AMD. Comparing the implementations, there's some peculiar differences that may matter:
intel_dp_extended_receiver_capabilities() is more "paranoid" than AMD DC's retrieve_link_cap() function in deciding if the extended receiver caps are valid. Intels implementation copies only the first 6 Bytes of extended receiver caps into the dpcd[] arrays, whereas AMD copies 16 Bytes. Not sure about the differences, but one of you may wanna check why this is, and if it matters somehow.
Btw. your proposed
/* blah */
if (max_rate > ...)
wouldn't work if dpcd[0x1] == 0xa, which it likely is [*]. AMD DC identified it as DP 1.1, eDP 1.3, and these extended caps seem to be only part of DP 1.3+ if i understand the comments in intel_dp_extended_receiver_capabilities() correctly.
-mario
--
Ville Syrjälä
Intel