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

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Date:   Tue, 28 May 2019 22:46:48 -0400
From:   Brian Masney <masneyb@...tation.org>
To:     Jeffrey Hugo <jeffrey.l.hugo@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Sean Paul <sean@...rly.run>, Rob Herring <robh@...nel.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        Dave Airlie <airlied@...ux.ie>,
        MSM <linux-arm-msm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>,
        Rob Clark <robdclark@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        freedreno@...ts.freedesktop.org
Subject: Re: [Freedreno] [PATCH RFC v2 0/6] ARM: qcom: initial Nexus 5
 display support

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
# busybox devmem 0xFD900714
0x00000000
# busybox devmem 0xFD900814
0x00000000
# busybox devmem 0xFD900914
0x00000000
# busybox devmem 0xFD900A14
0x00000000

I get the same values with the mainline kernel and 4.17.

Brian