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

[Maxime Ripard <maxime.ripard@bootlin.com>]

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On Fri, Jan 18, 2019 at 02:51:26PM +0000, Priit Laes wrote:
> On Fri, Jan 18, 2019 at 03:04:18PM +0100, Maxime Ripard wrote:
> > On Fri, Jan 18, 2019 at 10:10:53AM +0000, Priit Laes wrote:
> > > > > > > > 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?
> > > > > 
> > > > > Display is already connected via HDMI to the board. I don't really
> > > > > remove it, I just boot the device and let it start Xorg.
> > > > > Meanwhile I just ssh into the device and capture debugfs output.
> > > > > See my 3 testing scenarios below.
> > > > > 
> > > > > Kernel also includes one extra patch to fall back to DDC, in case HPD
> > > > > fails. Mostly the same I already submitted last November [1].
> > > > 
> > > > Do you have the same issue without that patch?
> > > 
> > > Can't really test this display without this patch and I do not have other
> > > HDMI/DVI screens. And this issue does not happen with other HDMI displays
> > > that I have here.
> > 
> > Can't you just force the monitor to be reported as present? It's not
> > great and we don't want to merge it, but that would allow you to test
> > that setup without too many interferences.
> 
> Baseline is clean u-boot / linux. U-boot does not detect/enable display.
> 
> 1) Booting Linux with drm.debug=0xe
> 
> * Linux does not detect/enable display
> 
> 2) Booting with drm.debug=0xe video=HDMI-A-1:640x480@60e
> 
> * Linux detects display, but display is garbled, and proper edid data is detected:
> 
> [snip]
> pll-video1                     0        0        0   327000000          0     0  50000
>    pll-video1-2x               0        0        0   654000000          0     0  50000
>       hdmi-tmds                0        0        0    25153846          0     0  50000
>          hdmi-ddc              0        0        0       89835          0     0  50000
> [/snip]
> 
> 3) Booting with drm.debug=0xe video=HDMI-A-1:640x480@60e
> And also one extra patch for Linux where HDMI DDC clock marked as critical
> 
> Linux detects and initializes display properly:
> [snip]
> pll-video1                     1        1        0   327000000          0     0  50000
>    pll-video1-2x               1        1        0   654000000          0     0  50000
>       hdmi-tmds                1        1        0    25153846          0     0  50000
>          hdmi-ddc              1        1        0       89835          0     0  50000
> [/snip]

I guess you'll need to track down when the hdmi-tmds and hdmi-ddc are
enabled and disabled, and if it makes sense :/

Maxime

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

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