imx-drm: screen flickering

imx-drm: screen flickering

[Christian Gmeiner]

Hi all.

>From time to time it happens that my LVDS display is flickering (look
at scroll bar in the video).
https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp=sharing

I really want to find the root cause of it, but I do not know where to
start. I can trigger this
sometimes after xscreensever "blanks" the screen and the screensafer
gets disabled
via user input.

Any hints?
--
Christian Gmeiner, MSc

imx-drm: screen flickering

[Christian Gmeiner]

2014-01-28 Christian Gmeiner <christian.gmeiner@gmail.com>:
> Hi all.
>
> From time to time it happens that my LVDS display is flickering (look
> at scroll bar in the video).
> https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp=sharing
>
> I really want to find the root cause of it, but I do not know where to
> start. I can trigger this
> sometimes after xscreensever "blanks" the screen and the screensafer
> gets disabled
> via user input.
>
> Any hints?

I forgot to add some details. I am using a 3.12.4 kernel with some a
some patches (dts, ..). As root filesystem
I am using debian 7 and this is how my xorg.conf looks like:

root at OT:/sys/kernel/debug# cat /etc/X11/xorg.conf
#
# DO NOT TOUCH - AUTOGENERATED FILE
#

Section "Device"
        Identifier      "Card0"
        Driver          "modesetting"

EndSection

Section "InputClass"
        Identifier      "keyboard layout"
        MatchIsKeyboard "on"
        MatchDevicePath "/dev/input/event*"
        Driver          "evdev"
        Option          "XkbLayout" "us"
EndSection


xscreensaver makes use of DPMS. So I think that the the problem could
be related to DPMS somehow.

greets
--
Christian Gmeiner, MSc

imx-drm: screen flickering

[Christian Gmeiner]

2014-01-28 Christian Gmeiner <christian.gmeiner@gmail.com>:
> 2014-01-28 Christian Gmeiner <christian.gmeiner@gmail.com>:
>> Hi all.
>>
>> From time to time it happens that my LVDS display is flickering (look
>> at scroll bar in the video).
>> https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp=sharing
>>
>> I really want to find the root cause of it, but I do not know where to
>> start. I can trigger this
>> sometimes after xscreensever "blanks" the screen and the screensafer
>> gets disabled
>> via user input.
>>
>> Any hints?
>
> I forgot to add some details. I am using a 3.12.4 kernel with some a
> some patches (dts, ..). As root filesystem
> I am using debian 7 and this is how my xorg.conf looks like:
>
> root at OT:/sys/kernel/debug# cat /etc/X11/xorg.conf
> #
> # DO NOT TOUCH - AUTOGENERATED FILE
> #
>
> Section "Device"
>         Identifier      "Card0"
>         Driver          "modesetting"
>
> EndSection
>
> Section "InputClass"
>         Identifier      "keyboard layout"
>         MatchIsKeyboard "on"
>         MatchDevicePath "/dev/input/event*"
>         Driver          "evdev"
>         Option          "XkbLayout" "us"
> EndSection
>
>
> xscreensaver makes use of DPMS. So I think that the the problem could
> be related to DPMS somehow.
>

I can trigger this with:
xset dpms force off; sleep 2; xset dpms force on

I need to execute this command less then 6 times to get the flickering.

greets
--
Christian Gmeiner, MSc

imx-drm: screen flickering

[Sascha Hauer]

Hi Christian,

On Tue, Jan 28, 2014 at 09:11:32AM +0100, Christian Gmeiner wrote:
> Hi all.
> 
> From time to time it happens that my LVDS display is flickering (look
> at scroll bar in the video).
> https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp=sharing
> 
> I really want to find the root cause of it, but I do not know where to
> start. I can trigger this
> sometimes after xscreensever "blanks" the screen and the screensafer
> gets disabled
> via user input.
> 
> Any hints?

Sorry, no idea. Philipp and me watched the video, but we both haven't
seen something like this before.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

imx-drm: screen flickering

[Marek Vasut]

On Wednesday, January 29, 2014 at 12:15:57 PM, Sascha Hauer wrote:
> Hi Christian,
> 
> On Tue, Jan 28, 2014 at 09:11:32AM +0100, Christian Gmeiner wrote:
> > Hi all.
> > 
> > From time to time it happens that my LVDS display is flickering (look
> > at scroll bar in the video).
> > https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp=sha
> > ring
> > 
> > I really want to find the root cause of it, but I do not know where to
> > start. I can trigger this
> > sometimes after xscreensever "blanks" the screen and the screensafer
> > gets disabled
> > via user input.
> > 
> > Any hints?
> 
> Sorry, no idea. Philipp and me watched the video, but we both haven't
> seen something like this before.

Isn't it the clock polarity being inverted thing again [1]?

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2013-
December/215536.html

The easiest way to check this would be to try sig_cfg.clk_pol = 0 or = 1 and see 
if it changes anything.

Best regards,
Marek Vasut

imx-drm: screen flickering

[Russell King - ARM Linux]

On Wed, Jan 29, 2014 at 03:53:14PM +0100, Marek Vasut wrote:
> Isn't it the clock polarity being inverted thing again [1]?
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2013-
> December/215536.html
> 
> The easiest way to check this would be to try sig_cfg.clk_pol = 0
> or = 1 and see if it changes anything.

It seems that the pixel clock polarity on iMX hardware is something of
a mess.  Some hardware blocks require one polarity, others require a
different polarity.

I think what would make sense is if the various output connectors/
encoders (in other words, imx-hdmi, imx-ldb, etc supplied their
properties concerning the clock polarity to the IPU layer.

We already have something like this in place already: we have the encoder
prepare functions calling into the ipuv3-crtc layer (via imx-drm-core) to
set the interface format, vsync/hsync pins, and clock flags - all of which
get used in the CRTC's mode_set method.  Adding the clock polarity into
that path doesn't sound too difficult.

The only issue is that there's a lack of conflict management here - but
that's not a new problem with this approach - it exists with the existing
data.

-- 
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up.  Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".

imx-drm: screen flickering

[Sascha Hauer]

On Wed, Jan 29, 2014 at 03:53:14PM +0100, Marek Vasut wrote:
> On Wednesday, January 29, 2014 at 12:15:57 PM, Sascha Hauer wrote:
> > Hi Christian,
> > 
> > On Tue, Jan 28, 2014 at 09:11:32AM +0100, Christian Gmeiner wrote:
> > > Hi all.
> > > 
> > > From time to time it happens that my LVDS display is flickering (look
> > > at scroll bar in the video).
> > > https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp=sha
> > > ring
> > > 
> > > I really want to find the root cause of it, but I do not know where to
> > > start. I can trigger this
> > > sometimes after xscreensever "blanks" the screen and the screensafer
> > > gets disabled
> > > via user input.
> > > 
> > > Any hints?
> > 
> > Sorry, no idea. Philipp and me watched the video, but we both haven't
> > seen something like this before.
> 
> Isn't it the clock polarity being inverted thing again [1]?

Could be, at least the result should look similar. I just wonder why it
only happens after a few times doing something. I would expect the clock
is always inverted then.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

imx-drm: screen flickering

[Marek Vasut]

On Thursday, January 30, 2014 at 08:45:26 AM, Sascha Hauer wrote:
> On Wed, Jan 29, 2014 at 03:53:14PM +0100, Marek Vasut wrote:
> > On Wednesday, January 29, 2014 at 12:15:57 PM, Sascha Hauer wrote:
> > > Hi Christian,
> > > 
> > > On Tue, Jan 28, 2014 at 09:11:32AM +0100, Christian Gmeiner wrote:
> > > > Hi all.
> > > > 
> > > > From time to time it happens that my LVDS display is flickering (look
> > > > at scroll bar in the video).
> > > > https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp
> > > > =sha ring
> > > > 
> > > > I really want to find the root cause of it, but I do not know where
> > > > to start. I can trigger this
> > > > sometimes after xscreensever "blanks" the screen and the screensafer
> > > > gets disabled
> > > > via user input.
> > > > 
> > > > Any hints?
> > > 
> > > Sorry, no idea. Philipp and me watched the video, but we both haven't
> > > seen something like this before.
> > 
> > Isn't it the clock polarity being inverted thing again [1]?
> 
> Could be, at least the result should look similar. I just wonder why it
> only happens after a few times doing something. I would expect the clock
> is always inverted then.

I actually noticed a rather strange behavior when the clock polarity was 
inverted as well. The flicker was not always there in my case either, but I used 
parallel LCD .

Best regards,
Marek Vasut

imx-drm: screen flickering

[Christian Gmeiner]

>
> On Thursday, January 30, 2014 at 08:45:26 AM, Sascha Hauer wrote:
> > On Wed, Jan 29, 2014 at 03:53:14PM +0100, Marek Vasut wrote:
> > > On Wednesday, January 29, 2014 at 12:15:57 PM, Sascha Hauer wrote:
> > > > Hi Christian,
> > > >
> > > > On Tue, Jan 28, 2014 at 09:11:32AM +0100, Christian Gmeiner wrote:
> > > > > Hi all.
> > > > >
> > > > > From time to time it happens that my LVDS display is flickering (look
> > > > > at scroll bar in the video).
> > > > > https://drive.google.com/file/d/0B_fznDimUHVubWtvVFlMTkdBbUU/edit?usp
> > > > > =sha ring
> > > > >
> > > > > I really want to find the root cause of it, but I do not know where
> > > > > to start. I can trigger this
> > > > > sometimes after xscreensever "blanks" the screen and the screensafer
> > > > > gets disabled
> > > > > via user input.
> > > > >
> > > > > Any hints?
> > > >
> > > > Sorry, no idea. Philipp and me watched the video, but we both haven't
> > > > seen something like this before.
> > >
> > > Isn't it the clock polarity being inverted thing again [1]?
> >
> > Could be, at least the result should look similar. I just wonder why it
> > only happens after a few times doing something. I would expect the clock
> > is always inverted then.
>
> I actually noticed a rather strange behavior when the clock polarity was
> inverted as well. The flicker was not always there in my case either, but I used
> parallel LCD .

I need to check this polarity thing again.

I found some time to look deeper into my screen flickering issue and
did some measurements.

green:   LVDS_0
blue:     LVDS_1
purple:  LVDS_2
yellow:  LVDS_Clk

https://drive.google.com/folderview?id=0B_fznDimUHVuWGZrT0puSldyZ1E&usp=sharing

In theory both measurements should look almost the same but for me it
looks like LVDS_0 and LVDS_1 are wrong.
IPU and LDB are - in my eyes - the only two components involved here.
So I had a look at the imx6 datasheet
and it could only be the IPU causing this kind of problems as the ldb
is does nothing really fancy here.
There is a IPU debug bus but there is quite almost no information on
how to use it. Also I am not sure if
it would help me to identify the issue.

greets
--
Christian Gmeiner, MSc

https://soundcloud.com/christian-gmeiner