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From:   Pintu Agarwal <pintu.ping@gmail.com>
Date:   Sun, 29 Sep 2019 22:24:19 +0530
Message-ID: <CAOuPNLgZ3kjBaCmXkXHZrncYqUxsNYKiXQqptoDBT_EWfjpNqg@mail.gmail.com>
Subject: Re: imx6: hdmi black screen issue after resume
To:     p.zabel@pengutronix.de, bob.beckett@collabora.com,
        dri-devel@lists.freedesktop.org,
        open list <linux-kernel@vger.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>, linux-pm@vger.kernel.org
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>
> On Mon, Sep 23, 2019 at 1:28 PM Pintu Agarwal <pintu.ping@gmail.com> wrote:
> >
> > Dear Philipp,
> >
> > I have a iMX6dl custom board with custom Linux Kernel 4.8.
> > I have both LCD and HDMI connected to the board.
> > And we are using weston/wayland as the display interface.
> > In normal boot, both LCD and HDMI display is working fine.
> >
> > But, currently, for one of the requirement, I am trying to explore and
> > support hibernation image booting on it.
> > Currently, we are able to resume the system without display.
> > Also, if we make the entire imx-drm as modules, and then install the
> > modules after resume, even LCD is also coming up.
> > But HDMI display is black out.
> >
> > After, resume, when I try to launch the weston, I noticed the following errors:
> > enabling vblank on crtc 0, ret: 0
> > drm_vblank_get: CALLED: vblank->refcount: 1
> > ------------[ cut here ]------------
> > WARNING: at drivers/gpu/drm/drm_atomic_helper.c:1121
> > drm_atomic_helper_wait_for_vblanks+0x228/0x24c [drm_kms_helper]()
> > [CRTC:24] vblank wait timed out
> > .....
> > [drm:drm_atomic_helper_commit_cleanup_done [drm_kms_helper]] *ERROR*
> > [CRTC:24:crtc-0] flip_done timed out
> >
> > ....
> > [00:06:42.600] Warning: computed repaint delay is insane: -5069 msec
> > [00:06:42.665] unexpectedly large timestamp jump (from 397522 to 402648)
> > ....
> >
> > And, when I try to reboot the system, the system does not reboot.
> > And I get the following error:
> > /wayland # reboot
> > ....
> > [17:55:01.180] destroy output while page flip pending
> > ...
> > imx-ipuv3 2400000.ipu: DC stop timeout after 50 ms
> >
> >
> > -------------
> > If you have any clue about this issue, please let me know.
> >
> > Any help will be really appreciated!
> >
> >
> > Thank You!
> >
> > Regards,
> > Pintu


Hi All,

I need some help, on the above issue.
Finally, I could boil down the issue to be vblank refcount issue.
After system resume, vblank ref count is getting screwed up, because
of which vblank_enable is not happening.
As per below code path: drivers/gpu/drm/drm_vblank.c:
drm_vblank_get()
{
[...]
/* Going from 0->1 means we have to enable interrupts again */
if (atomic_add_return(1, &vblank->refcount) == 1) {
    ret = drm_vblank_enable(dev, pipe);
} else {
    if (!vblank->enabled) {
        atomic_dec(&vblank->refcount);
        ret = -EINVAL;
    }
}
[...]
First time, everything seems fine.
drm_vblank_get: CALLED: pipe: 0, vblank->refcount: 0, vblank-enabled: 0
..
drm_vblank_enable: calling - enable_vblank
enabling vblank on crtc 0, ret: 0
...

But, after resume, somewhere during HDMI initialization, the refcount
is getting incremented.
drm_vblank_get: CALLED: pipe: 0, vblank->refcount: 1, vblank-enabled: 1
Thus, due to the above logic, drm_vblank_enable() will not be called,
if previous refcount is not 0.

What I further noticed is that, after resume, during hdmi_setup the
refcount is automatically getting updated.
drm_update_vblank_count - storing vblank count: diff: 1

This does not happen in normal case.
Now, I am not sure, why the vblank counter is getting incremented
during hdmi setup.
Is it like, hdmi setup is taking slightly longer time for
initialization, after resume??
Because of which the vblank timestamp counter is getting disturbed.

If anybody observed this issue, or aware about the fixes, please let me know.
It will be of great help.

Meanwhile, I am further continue to debug this more..

Regards,
Pintu