[linux-sunxi] Re: HDMI/DVI spurious failure

[Maxime Ripard]

Hi Priit,

On Wed, Jan 16, 2019 at 07:58:54AM +0000, Priit Laes wrote:
> > On Mon, Jan 14, 2019 at 01:29:34PM +0000, Priit Laes wrote:
> > > I have a somewhat curious case with one HDMI/DVI screen that fails
> > > to initialize properly every 6-7 boots. The display itself is also
> > > somewhat flawed (missing HPD pin and the VSYNC/HSYNC pulse width
> > > is set to 0 in EDID), but I suspect there could be some issues
> > > regarding timing in A20 HDMI driver in Linux.
> > > 
> ...
> 
> > It doesn't look related to the clock rate itself, since it doesn't
> > change between the two cases. However, in one case the DDC clock is
> > enabled and in the other it's disabled.
> > 
> > Was it taken at the same time? Maybe you can try with that patch?
> > http://code.bulix.org/z7jmkm-555344?raw
> 
> Thanks, after doing ~50+ boots I haven't seen a single failure.
> 
> Previously I had following failure cases which are now both fixed:
> 
> a) Linux without u-boot HDMI, where one in every 6-7 boots failed.
> b) u--boot with hdmi enabled switching to simplefb and then switching
> to kms, where previously all boots ended up with garbled screen.

So it's not really a fix, but it really looks like the clock is not
enabled when it should.

Can you describe your test scenario a bit more? What are you doing
exactly, just booting? When do you start using the display? When did
you capture the debugfs output that you pasted?

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com