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

[Marek Vasut]

On 10/11/24 5:10 AM, Liu Ying wrote:

Hi,

>>>> This Video PLL1 configuration since moved to &media_blk_ctrl {} , but it is still in the imx8mp.dtsi . Therefore, to make your panel work at the correct desired pixel clock frequency instead of some random one inherited from imx8mp.dtsi, add the following to the pollux DT, I believe that will fix the problem and is the correct fix:
>>>>
>>>> &media_blk_ctrl {
>>>>      // 506800000 = 72400000 * 7 (for single-link LVDS, this is enough)
>>>>      // there is no need to multiply the clock by * 2
>>>>      assigned-clock-rates = <500000000>, <200000000>, <0>, <0>, <500000000>, <506800000>;
>>>
>>> This assigns "video_pll1" clock rate to 506.8MHz which is currently not
>>> listed in imx_pll1443x_tbl[].
>>
>> Since commit b09c68dc57c9 ("clk: imx: pll14xx: Support dynamic rates") the 1443x PLLs can be configured to arbitrary rates which for video PLL is desirable as those should produce accurate clock.
> 
> Ack.
> 
>>
>>> Does the below patch[1] fix the regression issue? It explicitly sets
>>> the clock frequency of the panel timing to 74.25MHz.
>>>
>>> [1] https://patchwork.freedesktop.org/patch/616905/?series=139266&rev=1
>> That patch is wrong, there is an existing entry for this panel in panel-simple.c which is correct and precise, please do not add that kind of imprecise duplicate timings into DT.
> 
> At least the patch[1] is legitimate now to override the display
> timing of the panel because the override mode is something
> panel-simple.c supports.

It may be possible to override the mode, but why would this be the 
desired if the panel-simple.c already contains valid accurate timings 
for this particular panel ?

> And, pixel clock @74.25MHz is not out
> of the panel specification since edt_etml1010g3dra_timing
> indicates the minimum as 66.3MHz and the maximum as 78.9MHz.

The panel-simple.c already contains timings for this panel, which are 
accurate and follow the panel datasheet. If the goal here is to support 
approximate panel timings between the currently available three options 
(min/typ/max) listed in panel-simple, then that is another discussion 
for another patch.

> Furthermore, if "PHYTEC phyBOARD-Pollux i.MX8MP" also supports
> something like MIPI DSI to HDMI, then 74.25MHz panel pixel clock
> rate is more desirable because the LVDS display and the MIPI DSI
> display pipeline with typical 148.5MHz/74.25MHz pixel clock rates
> may use one single "video_pll1" clock.

I actually do have exactly this use case on one system -- one LVDS panel 
and one MIPI DSI panel -- the solution is really easy, source the LVDS 
pixel clock from Video PLL and the DSI clock from e.g. PLL3 .

> Anyway, I think it is ok to use the patch[1] or assigning
> "video_pll1" clock rate to 506.8MHz in DT(no things like MIPI
> DSI to HDMI in existing DT).
I believe for the current release, it is better to update the Video PLL 
clock in this one board DT, because that is minimum impact change 
isolated to this board and fixes a real issue where the LVDS panel 
worked within specification only by sheer chance.