On 09.09.24 5:00 AM, Peng Fan wrote:

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Subject: Re: i.MX8MP IMX-LCDIF Underrun Question(s)

On 06.09.24 3:46 AM, Adam Ford wrote:

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I have been testing various settings on the HDMI out of the i.MX8MP.

I noticed that sometimes my monitor would not sync, but sometimes

it

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would on the same resolution/refresh rate.  Frieder noted the LCDIF
was sometimes underflowing, so read up on it a little bit.

In the comments of the LCDIF driver, it's noted:
    Set FIFO Panic watermarks, low 1/3, high 2/3 .

However, in the downstream kernels, NXP changes the threshold to

1/2

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and 3/4 on the LCDIF that drives the HDMI, while leaving the other
LCDIF interfaces at the default.

When I increased the threshold to 1/2 and 3/4, it appeared that
several resolutions that my monitor was struggling to sync started
working, and it appeared to sync faster.  I don't have an HDMI
analyzer, so I cannot verify much beyond knowing if my monitor can

or

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cannot sync.

For me this change doesn't seem to cause any improved behavior. My
monitor still fails to sync every few times I run "modetest -s" .

Also we have a downstream kernel based on 6.1 with backported
HDMI support and I don't see the issues there. But I need to make
some further tests to make any reliable statements.

Downstream kernel has some NOC settings that not supported
in upstream kernel, that maybe the issue.

If you check 6.6 kernel, you could see some noc related settings
in imx8mp-blk-ctl.c imx8m-blk-ctl.c and gpcv2.c. You may give a
try with those noc settings applied and see whether that would
improve.

With "downstream kernel" I didn't mean linux-imx. I meant our Kontron
linux-ktn, which is based on mainline. I didn't test linux-imx to see if
the issue occurs there, but that might be one task for further debugging.