Re: [PATCH] drm/i915/skl: Support Y tiling in MMIO flips

From: Daniel Vetter <daniel@ffwll.ch>
To: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, Intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915/skl: Support Y tiling in MMIO flips
Date: Mon, 20 Apr 2015 10:24:20 -0700	[thread overview]
Message-ID: <20150420172420.GK14565@bremse> (raw)
In-Reply-To: <55352B7C.7080406@linux.intel.com>

On Mon, Apr 20, 2015 at 05:38:20PM +0100, Tvrtko Ursulin wrote:
> 
> On 04/20/2015 05:22 PM, Daniel Vetter wrote:
> >On Mon, Apr 20, 2015 at 04:22:48PM +0100, Tvrtko Ursulin wrote:
> >>From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>
> >>Add Y tiling support to skl_do_mmio_flip.
> >>
> >>Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>Cc: Damien Lespiau <damien.lespiau@intel.com>
> >>Cc: Sonika Jindal <sonika.jindal@intel.com>
> >>Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> >>---
> >>Looks like we completely missed this completely parallel instance of plane
> >>programming code when working on Y tiling support!
> >>
> >>Will rotation need supporting here as well?
> >
> >Oh dear this is a bit ugly. We definitely need either this for 4.1 or take
> >out the Y-tiling support for 4.1. Rotation only made 4.2, so I think
> >we're good, but we do indeed need to take rotation into account here too.
> 
> What is ugly, this patch or the overall situation?

The situation, since catching this kind of stuff is why we should have a
real userspace implementation ;-)

> >And it seems like we also need a pile of igt testcases to make sure
> >Y-tiling, rotation (even 180 probably) works correctly with pageflips. Yay
> >for kms_flip growing even more.
> 
> I added Y to kms_flip_tiling back then - but both that one and kms_flip
> don't do any pipe crc. So not much use in automated fashion. And testdisplay
> apparently does not hit this path.
> 
> I did not have working crc hw back then, maybe that has changed, I'll check
> it and then, depending on the outcome, see if I can add something automated.

Hm right we'd need a real crc based testcase, not just exercising the
codepaths. Simplest solution might be to extend the rotation test with a
new subtests which does a pageflip before sampling the crc. Adding crc
checks to the kms_flip monster is probably not a good idea.

> Either way, adding this fix sounds better than reverting everything.

I don't mean to revert everything, just disable the feature in case we
can't fix it up properly.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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