Re: [PATCH v2 5/6] drm/panel: st7703: Drive XBD599 panel at higher clock rate

Maxime Ripard
2024-02-08T19:05:11Z

[-- Attachment #1: Type: text/plain, Size: 1391 bytes --]

Hi Frank,

On Mon, Feb 05, 2024 at 04:22:28PM +0100, Frank Oltmanns wrote:
> This panel is used in the pinephone that runs on a Allwinner A64 SOC.
> The SOC requires pll-mipi to run at more than 500 MHz.
>
> This is the relevant clock tree:
> pll-mipi
> tcon0
> tcon-data-clock
>
> tcon-data-clock has to run at 1/4 the DSI per-lane bit rate. The XBD599
> has 24 bpp and 4 lanes. Therefore, the resulting requested
> tcon-data-clock rate is:
> crtc_clock * 1000 * (24 / 4) / 4
>
> tcon-data-clock runs at tcon0 / 4 (fixed divisor), so it requests a
> parent rate of
> 4 * (crtc_clock * 1000 * (24 / 4) / 4)
>
> Since tcon0 is a ccu_mux, the rate of tcon0 equals the rate of pll-mipi.
>
> pll-mipi's constraint to run at 500MHz or higher forces us to have a
> crtc_clock >= 83333 kHz if we want a 60 Hz vertical refresh rate.
>
> Change [hv]sync_(start|end) so that we reach a clock rate of 83502 kHz
> so that it is high enough to align with pll-pipi limits.
>
> Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>

That commit log is great, but it's kind of off-topic. It's a panel
driver, it can be used on any MIPI-DSI controller, the only relevant
information there should be the panel timings required in the datasheet.

The PLL setup is something for the MIPI-DSI driver to adjust, not for
the panel to care for.

Maxime

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]