i.MX8MP IMX-LCDIF Underrun Question(s)

[Frieder Schrempf]

On 09.09.24 5:00 AM, Peng Fan wrote:
>> Subject: Re: i.MX8MP IMX-LCDIF Underrun Question(s)
>>
>> On 06.09.24 3:46 AM, Adam Ford wrote:
>>> 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
>>> 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
>>> 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
>>> 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.