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From: Brian Masney <masneyb@onstation.org>
To: Jeffrey Hugo <jhugo@codeaurora.org>
Cc: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>,
	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
Date: Wed, 29 May 2019 17:54:21 -0400	[thread overview]
Message-ID: <20190529215421.GA20611@basecamp> (raw)
In-Reply-To: <26c535af-9853-c8c9-3138-04f5d9ee11b0@codeaurora.org>

On Wed, May 29, 2019 at 01:58:16PM -0600, Jeffrey Hugo wrote:
> On 5/29/2019 1:30 PM, Brian Masney wrote:
> > 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!
> 
> Awesome.  I'm glad it was something simple.
> 
> > 
> > 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?
> > 
> 
> Short version, yes.  Long version:
> 
> I still have that hack in my tree and haven't come back to formulating
> a proper fix yet.  Feel free to run with it.
> 
> Thinking about it briefly, we could do two things.  We could fake a
> hardware counter by just increment an int every time the vblank irq is
> processed, but that seems clunky.  Otherwise, we could force a
> fallback onto the timestamp solution, which seems less invasive.
> 
> In theory, we could service multiple displays, with different
> properties (ie a combination of command and video mode).  The hack
> then, is not good, because it would break video mode (at-least we
> wouldn't be using the register when we could).  It would be great if
> the use of the hardware register could be done per display.
> 
> Luckily, it looks like someone just made that possible -
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/gpu/drm/drm_vblank.c?h=v5.2-rc2&id=ed20151a7699bb2c77eba3610199789a126940c4

I'll work on this for the msm driver.

Thanks for the info!

Brian

  reply	other threads:[~2019-05-29 21:54 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-09  2:03 Brian Masney
2019-05-09  2:03 ` [PATCH v2 1/6] drm: msm: remove resv fields from msm_gem_object struct Brian Masney
2019-05-13 20:32   ` Bjorn Andersson
2019-05-13 22:25     ` Brian Masney
2019-05-09  2:03 ` [PATCH RFC v2 2/6] drm: msm: add dirty framebuffer helper Brian Masney
2019-05-09  2:03 ` [PATCH v2 3/6] ARM: qcom_defconfig: add display-related options Brian Masney
2019-05-09  2:03 ` [PATCH v2 4/6] ARM: dts: msm8974: add display support Brian Masney
2019-05-09  2:03 ` [PATCH v2 5/6] ARM: dts: qcom: msm8974-hammerhead: add support for backlight Brian Masney
2019-05-09  2:03 ` [PATCH v2 6/6] ARM: dts: qcom: msm8974-hammerhead: add support for display Brian Masney
2019-05-09  2:06 ` [PATCH RFC v2 0/6] ARM: qcom: initial Nexus 5 display support Brian Masney
2019-05-28 13:46 ` Linus Walleij
2019-05-29  1:17   ` Brian Masney
2019-05-29  1:32     ` [Freedreno] " Jeffrey Hugo
2019-05-29  1:37       ` Brian Masney
2019-05-29  1:42         ` Jeffrey Hugo
2019-05-29  2:46           ` Brian Masney
     [not found]             ` <CAOCk7NpC93ACr4jFm7SBOKSvFJSDhq2byX6BAYPX29BuYEkWnQ@mail.gmail.com>
2019-05-29 10:28               ` Brian Masney
2019-05-29 14:41                 ` Jeffrey Hugo
2019-05-29 19:30                   ` Brian Masney
2019-05-29 19:58                     ` Jeffrey Hugo
2019-05-29 21:54                       ` Brian Masney [this message]
2019-05-29  2:14     ` Rob Clark
2019-05-29  2:24       ` [Freedreno] " Jeffrey Hugo
2019-05-29  6:23     ` Linus Walleij
2019-05-29  9:41       ` Brian Masney

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