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

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Message-ID: <YTenPMOOepGo2ZU8@smile.fi.intel.com>
Date:   Tue, 7 Sep 2021 20:54:04 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Chris Morgan <macroalpha82@...il.com>
Cc:     abel.vesa@....com, festevam@...il.com, heiko@...ech.de,
        kernel@...gutronix.de, lee.jones@...aro.org, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-imx@....com,
        linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        mturquette@...libre.com, rafael.j.wysocki@...el.com,
        rjw@...ysocki.net, s.hauer@...gutronix.de, sboyd@...nel.org,
        shawnguo@...nel.org, zhangqing@...k-chips.com,
        Chris Morgan <macromorgan@...mail.com>
Subject: Re: [PATCH v4 1/4] clk: fractional-divider: Export approximation
 algorithm to the CCF users

On Tue, Sep 07, 2021 at 10:44:00AM -0500, Chris Morgan wrote:
> From: Chris Morgan <macromorgan@...mail.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.

-- 
With Best Regards,
Andy Shevchenko