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Date:   Wed, 29 May 2019 15:30:46 -0400
From:   Brian Masney <masneyb@onstation.org>
To:     Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Sean Paul <sean@poorly.run>, Rob Herring <robh@kernel.org>,
        Jonathan Marek <jonathan@marek.ca>,
        Dave Airlie <airlied@linux.ie>,
        MSM <linux-arm-msm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
        Rob Clark <robdclark@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        freedreno <freedreno@lists.freedesktop.org>
Subject: Re: [Freedreno] [PATCH RFC v2 0/6] ARM: qcom: initial Nexus 5
 display support
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On Wed, May 29, 2019 at 08:41:31AM -0600, Jeffrey Hugo wrote:
> On Wed, May 29, 2019 at 4:28 AM Brian Masney <masneyb@onstation.org> wrote:
> >
> > On Tue, May 28, 2019 at 08:53:49PM -0600, Jeffrey Hugo wrote:
> > > On Tue, May 28, 2019 at 8:46 PM Brian Masney <masneyb@onstation.org> wrote:
> > > >
> > > > On Tue, May 28, 2019 at 07:42:19PM -0600, Jeffrey Hugo wrote:
> > > > > > > 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.
> > > > >
> > > > > Actually, the ping pong element exists in both modes, but 'pp done
> > > > > time out' is a good indicator that it is command mode.
> > > > >
> > > > > Are you also seeing vblank timeouts?
> > > >
> > > > Yes, here's a snippet of the first one.
> > > >
> > > > [    2.556014] WARNING: CPU: 0 PID: 5 at drivers/gpu/drm/drm_atomic_helper.c:1429 drm_atomic_helper_wait_for_vblanks.part.1+0x288/0x290
> > > > [    2.556020] [CRTC:49:crtc-0] vblank wait timed out
> > > > [    2.556023] Modules linked in:
> > > > [    2.556034] CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.2.0-rc1-00178-g72c3c1fd5f86-dirty #426
> > > > [    2.556038] Hardware name: Generic DT based system
> > > > [    2.556056] Workqueue: events deferred_probe_work_func
> > > > ...
> > > >
> > > > > Do you have busybox?
> > > > >
> > > > > Can you run -
> > > > > sudo busybox devmem 0xFD900614
> > > > > sudo busybox devmem 0xFD900714
> > > > > sudo busybox devmem 0xFD900814
> > > > > sudo busybox devmem 0xFD900914
> > > > > sudo busybox devmem 0xFD900A14
> > > >
> > > > # busybox devmem 0xFD900614
> > > > 0x00020020
> > >
> > > Ok, so CTL_0 path, command mode, ping pong 0, with the output going to DSI 1.
> > >
> > > Next one please:
> > >
> > > busybox devmem 0xFD912D30
> >
> > It's 0x00000000 on mainline and 4.17. I used the following script to
> > dump the entire mdp5 memory region and attached the dump from 4.17 and
> > 5.2rc1.
> >
> 
> ok, 0 means autorefresh is not on.  Which is fine.  My next guess
> would be the vblank code checking the hardware vblank counter, which
> doesn't exist.
> In video mode, there is a frame counter which increments, which can be
> used as the vblank counter.  Unfortunately, that hardware isn't active
> in command mode, and there isn't an equivalent.
> 
> So, the vblank code is going to read the register, and look for an
> update, which will never happen, thus it will timeout.  There is a
> backup path which uses timestamps (no hardware), which you can
> activate with a quick hack - make max_vblank_count = 0 at the
> following line
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/msm/disp/mdp5/mdp5_kms.c#L753

That fixed the issue!

I previously observed that mdp5_get_vblank_counter, specifically
mdp5_encoder_get_framecount, would always return 0.

What's the best way to fix this in mainline? Set that to zero if any
of the interface modes is MDP5_INTF_DSI_MODE_COMMAND?

Brian