Re: [Bug Report] DU: Error messages at boot log and can't show image on RGB Display.

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hello Hiep-san,

Sorry for the late reply.

On Thursday 14 May 2015 12:18:21 Cao Minh Hiep wrote:
> Hi Laurent-san,
> 
> I'd like to report some more informations
> 
> On 2015年05月14日 06:56, Laurent Pinchart wrote:
> > On Wednesday 13 May 2015 15:43:36 Cao Minh Hiep wrote:
> >> Hi All.
> >> 
> >> We are testing Linux upstream version-4.1-rc2 on Lager.
> >> We found a Error message of DU(Display Unit) at boot logs:
> >> The Warning messages is showed as below:
> >> "rcar-du feb00000.display: encoder initialization failed, skipping"
> >> Then we tried to show a .bmp image on RGB Display via RGB port. But it
> >> didn't work.
> >> 
> >> Testing method:
> >> 1. Connect RGB Display to RGB port on Lager.
> >> 2. Show a BMP image on Display by this command:
> >> # bmap /dev/fb0 ./image.bmp
> >> 
> >> We'd like to report this problem first.
> >> There are no error message at version v4.0 stable.
> >> And showed the image on RGB Display normally at version v4.0 stable.
> >> We are looking for the error patch that added between v4.0 and v4.1-rc2.
> > 
> > I've tried v4.1-rc2 and haven't experienced that problem. It might be
> > related to kernel configuration, could you please share your .config file
> > ?
>
> We found that, if revert these patches then rebuild kernel, the error
> logs "encoder initialization failed..." will be disappeared:
> 26c00ab ARM: shmobile: lager: Add DU external pixel clocks to DT
> fd25cdd ARM: shmobile: lager: Add DU HDMI output support
> These patch added between v4.0 and v4.1-rc2.
> But with this test, a bmp image still could not show on RGB Display.

The error message isn't fatal. It's caused by HDMI support being disabled for 
the rcar-du driver, so the driver warns that the HDMI encoder can't be 
initialized.

I'll submit a patch that adds the encoder name to the error message to ease 
debugging, but the message itself is normal. The driver should initialize all 
the other encoders properly.

I've retested this on a stock v4.1-rc2 kernel with the kernel configuration 
file you've provided. I can reproduce the error message, and then noticed a 
potential kernel crash caused by a bug in the rcar-du driver. I have submitted 
a patch to fix it (and have CC'ed you).

With the fix applied I can use the DU normally with the modetest application. 
I've also tested the fbdev compat layer, and can confirm that you won't get an 
output on the screen if you don't configure the display first. This can be 
done through the KMS API or the FBDEV API (FBIOPUT_VSCREENINFO).

-- 
Regards,

Laurent Pinchart