Re: [PATCH v4 1/4] clk: fractional-divider: Export approximation algorithm to the CCF users

Andy Shevchenko
2021-09-07T17:54:13Z

On Tue, Sep 07, 2021 at 10:44:00AM -0500, Chris Morgan wrote:
> From: Chris Morgan <macromorgan@hotmail.com>
>
> Unfortunately, I can confirm this breaks the DSI panel on the Rockchip
> PX30 (and possibly other SoCs). Tested on my Odroid Go Advance. When
> I revert 4e7cf74fa3b2 "clk: fractional-divider: Export approximation
> algorithm to the CCF users" and 928f9e268611 "clk: fractional-divider:
> Hide clk_fractional_divider_ops from wide audience" the panel begins
> working again as expected on the master branch.
>
> It looks like an assumption is made in the vop_crtc_mode_fixup()
> function in the rockchip_drm_vop.c that gets broken with this change.
> Specifically, the function says in the comments "When DRM gives us a
> mode, we should add 999 Hz to it.". I believe this is no longer true
> after this clk change, and when I remove the + 999 from the function
> the DSI panel works again. Note that I do not know the implications
> of removing this 999 aside from that it fixes the DSI panel on my
> PX30 after this change, so I don't know if it's a positive change
> or not.
>
> Thank you.

Thank you for the report!

I'll check this. Perhaps Heiko can help with testing as well on his side.