Re: [PATCH v4 2/2] drm: lcdif: Add support for i.MX8MP LCDIF variant

[Marek Vasut <marex@denx.de>]

On 5/30/22 11:27, Alexander Stein wrote:
> Hi Marek,

Hi,

[...]

> I got this working, somehow. The root cause was that the LDB clock was not the
> media_disp2_pix_root_clk clock * 7, which is mandatory for LVDS (single link).
> 
> excerpt from clk_summary:
> video_pll1_out     2 2 0   594000000          0     0  50000         Y
>     media_ldb       1 1 0   594000000          0     0  50000         Y
>     media_disp2_pix 1 1 0    66000000          0     0  50000         Y
> 
> media_ldb is too high (should be 462000000). I wonder why media_ldb is not a
> child from media_disp2_pix (or vice versa) when there is a hard dependency.

Probably that's a matter of imx8mp.dtsi patch ?

> There are several solutions:
> 1.
> Set video_pll1 to 1039500000 and adjust requested pixel clock of the panel
> (74250000 in this case). Now the dividers match hit the clock rates exactly.
> But this renders the display list in panel-simple a bit useless.
> 
> 2.
> Adjust video_pll1_out only (e.g. 478757145). Now the calculated clocks comply
> to their mandated ratio. But this might affect other users, e.g. DSI displays
> 
> 3.
> Improve fsl_ldb_atomic_check to set adjusted_mode.clock to an achievable
> clock. This way lcdif will pick the new pixelclock to match their ratio.
> But there is more work necessary, e.g. ensure the new pixelclock is in the
> valid range of the display.

So far, I'm adjusting the LDB clock to match the panel in DT, but that 
indeed could use an improvement.

> To summarize:
> For both HDMI and LVDS using changes unrelated to this lcdif driver:
> Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>

Thanks