Re: [Freedreno] [PATCH RFC v2 0/6] ARM: qcom: initial Nexus 5 display support

[Brian Masney]

On Tue, May 28, 2019 at 07:32:14PM -0600, Jeffrey Hugo wrote:
> On Tue, May 28, 2019 at 7:17 PM Brian Masney <masneyb@xxxxxxxxxxxxx> wrote:
> >
> > On Tue, May 28, 2019 at 03:46:14PM +0200, Linus Walleij wrote:
> > > On Thu, May 9, 2019 at 4:04 AM Brian Masney <masneyb@xxxxxxxxxxxxx> wrote:
> > >
> > > > Here is a patch series that adds initial display support for the LG
> > > > Nexus 5 (hammerhead) phone. It's not fully working so that's why some
> > > > of these patches are RFC until we can get it fully working.
> > > >
> > > > The phones boots into terminal mode, however there is a several second
> > > > (or more) delay when writing to tty1 compared to when the changes are
> > > > actually shown on the screen. The following errors are in dmesg:
> > >
> > > I tested to apply patches 2-6 and got the console up on the phone as well.
> > > I see the same timouts, and I also notice the update is slow in the
> > > display, as if the DSI panel was running in low power (LP) mode.
> > >
> > > Was booting this to do some other work, but happy to see the progress!
> >
> > Thanks!
> >
> > I've had three people email me off list regarding the display working on
> > 4.17 before the msm kms/drm driver was converted to the DRM atomic API so
> > this email is to get some more information out publicly.
> >
> > I pushed up a branch to my github with 15 patches applied against 4.17
> > that has a working display:
> >
> > https://github.com/masneyb/linux/commits/display-works-4.17
> >
> > It's in low speed mode but its usable. The first 10 patches are in
> > mainline now and the last 5 are in essence this patch series with the
> > exception of 'drm/atomic+msm: add helper to implement legacy dirtyfb'.
> > There's a slightly different version of that patch in mainline now.
> >
> > I'm planning to work on the msm8974 interconnect support once some of
> > the outstanding interconnect patches for the msm kms/drm driver arrive
> > in mainline. I'd really like to understand why the display works on
> > 4.17 with those patches though. I assume that it's related to the
> > vblank events not working properly? Let me preface this with I'm a
> > total DRM newbie, but it looked like the pre-DRM-atomic driver wasn't
> > looking for these events in the atomic commits before the migration?
> > See commit 70db18dca4e0 ("drm/msm: Remove msm_commit/worker, use atomic
> > helper commit"), specifically the drm_atomic_helper_wait_for_vblanks()
> > call that was added.
> 
> Do you know if the nexus 5 has a video or command mode panel?  There
> is some glitchyness with vblanks and command mode panels.

Its in command mode. I know this because I see two 'pp done time out'
messages, even on 4.17. Based on my understanding, the ping pong code is
only applicable for command mode panels.

Brian