Message-ID: <bd884164-3a38-446d-8a54-3d716a3e0360@denx.de>
Date: Sat, 23 Nov 2024 21:11:58 +0100
From: Marek Vasut <marex@...x.de>
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Subject: Re: [PATCH v7 2/7] Revert "clk: imx: clk-imx8mp: Allow media_disp
 pixel clock reconfigure parent rate"

On 11/22/24 4:39 AM, Ying Liu wrote:
> On 11/22/24, Marek Vasut wrote:
>> On 11/20/24 7:38 AM, Ying Liu wrote:
>>
>> [...]
>>
>>>>> If the DP monitors support typical video modes like 1080p60 with
>>>>> 148.5MHz pixel clock rate, I assume these typical video modes work
>>>>> still ok with this patch at least.  Please help confirm this, since if the
>>>>> alternative solution(*) doesn't stand, we would know those video
>>>>> modes still work ok with my solution(fixed PLL rate).
>>>>
>>>> They do not work with the fixed PLL setting.
>>>
>>> Why?  Did you assign a sensible fixed PLL rate in DT?
>>
>> Whatever was in imx8mp.dtsi does not really work for all the panels.
>> Please keep in mind that the use case I have does not include only
>> 1920x1080 "standard" panels, but also other resolutions.
> 
> It looks like you are still sticking to the idea of supporting all potentially
> valid video modes by trying to find an "alternative" solution, while
> neglecting that the solution *could be* never working.

Reconfiguring the PLL to achieve accurate pixel clock is working 
already, right now.

>>> Can you please compare clk_summary output for the failing cases
>>> before and after this patch is applied? I assume that if you use
>>> the fixed PLL rate same to the rate which works before this patch is
>>> applied, the typical video modes still just work after this patch is
>>> applied.
>>
>> I'm afraid I do not need to support only typical video modes, but also
>> the other "atypical" modes.
> 
> If the "alternative" solution doesn't work, we'll end up using the "fixed
> PLL rate" solution.  It that case, some video modes would be filtered
> out as a sacrifice.

Maybe it would be better to continue the discussion in

[PATCH 0/5] clk: Fix simple video pipelines on i.MX8

which seems close to the alternative solution I was looking for ?

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