[PATCH v2] drm/panel: Set max rate for Ilitek ILI9881C

[Linus Walleij]

On Tue, Nov 20, 2018 at 12:02 PM Andrzej Hajda <a.hajda at samsung.com> wrote:

> Anyway more I think about it more doubts I have. hs_rate can be helpful
> for command mode panels - panel refresh rate (provided by timings)
> imposes only lower limit on the speed, max hs rate will impose upper limit.
>
> In case of video mode, timings determines exactly value of the clock, so
> max hs rate is unnecessary, am I right?

I looked closer at the code for a particular DSI panel, the Sony
ACX424AKP.

This panel can be used in both command and video mode.

In the command mode, the panel support much higher speed,
but in video mode it is restricted to a lower speed by the
resolution timings:

#define VID_MODE_REFRESH_RATE   60
#define DSI_HS_FREQ_HZ_VID      330000000
#define DSI_HS_FREQ_HZ_CMD      420160000
#define DSI_LP_FREQ_HZ          19200000

(From outoftree code as usual, I might make a proper panel
driver for this display too...)

So I think there is a need for both, especially for this kind
of dual-mode panels, but hs_rate is likely always
>= the vide mode rate.

Yours,
Linus Walleij