Re: [PATCH] drm: lcdif: Use adjusted_mode .clock instead of .crtc_clock

[Marek Vasut <marex@denx.de>]

On 10/7/24 7:01 PM, Isaac Scott wrote:
> Hi Marek,

Hi,

> On Sat, 2024-07-06 at 02:16 +0200, Marek Vasut wrote:
>> On 6/24/24 11:19 AM, Alexander Stein wrote:
>>> Am Freitag, 31. Mai 2024, 22:27:21 CEST schrieb Marek Vasut:
>>>> In case an upstream bridge modified the required clock frequency
>>>> in its .atomic_check callback by setting adjusted_mode.clock ,
>>>> make sure that clock frequency is generated by the LCDIFv3 block.
>>>>
>>>> This is useful e.g. when LCDIFv3 feeds DSIM which feeds TC358767
>>>> with (e)DP output, where the TC358767 expects precise timing on
>>>> its input side, the precise timing must be generated by the
>>>> LCDIF.
>>>>
>>>> Signed-off-by: Marek Vasut <marex@denx.de>
>>>
>>> With the other rc358767 patches in place, this does the trick.
>>> Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
>>
>> I'll pick this up next week if there is no objection.
> 
> Unfortunately, this has caused a regression that is present in v6.12-
> rc1 on the i.MX8MP PHYTEC Pollux using the
> arch/arm64/boot/dts/freescale/imx8mp-phyboard-pollux-rdk.dts. The
> display is the edt,etml1010g3dra panel, as per the upstream dts. We
> bisected to this commit, and reverting this change fixed the screen.
> 
> We then tried to retest this on top of v6.12-rc2, and found we also had
> to revert commit ff06ea04e4cf3ba2f025024776e83bfbdfa05155 ("clk: imx:
> clk-imx8mp: Allow media_disp pixel clock reconfigure parent rate")
> alongside this. Reverting these two commits makes the display work
> again at -rc2.
> 
> Do you have any suggestions on anything we might be missing on our end?
> Please let me know if there's anything you'd like me to test as I'm not
> sure what the underlying fault was here.
I believe what is going on is that the LCDIF cannot configure its 
upstream clock because something else is already using those clock and 
it set those clock to a specific frequency. LCDIF is now trying to 
configure those clock to match the LVDS panel, and it fails, so it tries 
to set some approximate clock and that is not good enough for the LVDS 
panel.

Can you share dump of /sys/kernel/debug/clk/clk_summary on failing and 
working system ? You might see the difference around the "video" clock.

(I have seen this behavior before, the fix was usually a matter of 
moving one of the LCDIFs to another upstream clock like PLL3, so it can 
pick well matching output clock instead of some horrid approximation 
which then drives the panel likely out of specification)