[Intel-gfx] [PATCH] drm/i915: Prune 2560x2880 mode for 5K tiled dual DP monitors

[Manasi Navare]

On Tue, Sep 10, 2019 at 12:20:05PM +0300, Jani Nikula wrote:
> On Mon, 09 Sep 2019, Manasi Navare <manasi.d.navare at intel.com> wrote:
> > On Thu, Sep 05, 2019 at 11:03:12AM +0530, Nautiyal, Ankit K wrote:
> >> Hi,
> >> 
> >> I was able to get 5K HPz27q 317b monitor for some time. Below are the
> >> observation on HPz27q Monitor with two DP cables connected to a KBL machine.
> >> 
> >> *****General Observation*****
> >> The monitor settings has two modes, DP1.0 and DP1.2.
> >> One of the connector is enumerated as 'tiled' and the other as non tiled.
> >> 
> >> The non-tiled connector has modes starting from 2K and below, and the tiled
> >> connector has just one mode 2560x2880.
> >> No corruption observed in this case.
> >> 
> >> In case of DP2.0 two connectors are enumerated, both tiled.
> >> One connector has modes from 3849x2160 and below. 2560x2880 being preferred
> >> mode.
> >> The other has 2560x2880 mode, also preferred.
> >> 
> >> The issue is seen when both the modes selected are 2560x2880. This results
> >> like two halves of screens not in sync.
> >> 
> >> *****Experiment with different patches*****
> >> 
> >> As discussed I collected logs in 3 cases:
> >> 1. Without any patch (vanilla)
> >> 2. With patch to prune the 2560x2880 mode, only for tile with HLOC and VLOC
> >> as 0.
> >> 3. With a patch to force the connector property as 'false'
> >> 
> >> Logs for which are attached in fdo bug #97244
> >> https://bugs.freedesktop.org/show_bug.cgi?id=97244
> >> https://bugs.freedesktop.org/attachment.cgi?id=145267
> >> 
> >> Note 1: I had changed the display info to provide the Tile information, in
> >> case the connector 'has_tile' is true.
> >> Note 2: I had checked and collected logs with single display and also with
> >> dual display configuration with DP1.2 monitor settings.
> >> Note 3: The mode is changed using xrandr.
> >> 
> >> case1:
> >> -Without any patch : 2560x2880 modeset on both connectors causes corruption.
> >> 
> >> case2:
> >> -With 2560x2880 mode pruned for one of the tile : Only one of the connector
> >> shows 2560x2880 mode.
> >> 2560x2880 modeset on any the remaining connector resulted in blank screen.
> >> Any other modeset works.
> >> 
> >> case3:
> >> -With has_tile connector property forcibly reset : The connector are listed
> >> as not tiled but still, 2560x2880 modeset on any the connectors causes blank
> >> screen.
> >> Any other modeset works.
> >> 
> >> To summarize, pruning on just one tiled connector does not solve the issue,
> >> if we need to prune, we need to do it for both the connectors.
> >> Secondly, the forcible setting of has_tile = 'false' also, does not help,
> >> and resulted in blank screen when 2560x2880 mode is applied.
> >> So IMHO if we need to prune the mode 2560x2880, we need to prune it for both
> >> the connectors.
> >>
> >
> > Thanks Ankit for these experiments and logs.
> > So looks like the solution would be to add a quirk for thsi specific EDID for
> > the panel and then  prune 2560x2880 on both connectors.
> >
> > Jani does that sound like a good acceptable solution?
> 
> So you'd have to disable the mode for both displays, but then it would
> seem odd to expose the tiling configuration with a non-existing mode,
> wouldn't it?
> 
> The quirk should be: on these displays, disable tiling and prune the
> modes listed in the tile info. That's a fairly generic quirk that makes
> sense to *define* in drm. However you'd only *implement* that quirk in
> affected drivers, i.e. i915.
> 
> The question remains, what does it take to actually fix this? I haven't
> looked at the patches in detail, what makes them so icl specific?
>

This made me go back and reconnect with the HW teams and get some clarifications.
Looks like the transcoder port sync feature for DP SST was added since BDW
and only the MST support starts from ICL+, but this was not clearly called out
in the bspec and hence the confusion.

I will update my transcoder port sync patches : https://patchwork.freedesktop.org/series/66403/
to add this support starting BDW
and Ankit you could then test it on the 5K monitor and it should fix it.

Manasi
 
> I'll repeat what I said up-thread:
> 
> On Wed, 28 Aug 2019, Jani Nikula <jani.nikula at linux.intel.com> wrote:
> > Finally, and perhaps most importantly, there are people on the bug that
> > are going to be rather underwhelmed that after three years they get a
> > patch that simply rejects the very mode that was the reason for buying
> > the display they have. Insult to injury, the real fix is for a platform
> > that didn't exist when they bought the displays.
> 
> Some of those folks apparently can actually make it work when they try
> hard enough. You'd take that away too.
> 
> 
> BR,
> Jani.
> 
> 
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center