Re: [PATCH] clk: qcom: dispcc-sc8280xp: remove CLK_SET_RATE_PARENT from byte_div_clk_src dividers

[Brian Masney <bmasney@redhat.com>]

Hi Pengyu and Konrad,

On Tue, Mar 03, 2026 at 01:10:43PM +0100, Konrad Dybcio wrote:
> On 3/3/26 12:55 PM, Pengyu Luo wrote:
> > From: White Lewis <liu224806@gmail.com>
> > 
> > The four byte_div_clk_src dividers (disp{0,1}_cc_mdss_byte{0,1}_div_clk_src)
> > had CLK_SET_RATE_PARENT set. When the DSI driver calls clk_set_rate() on
> > byte_intf_clk, the rate-change propagates through the divider up to the
> > parent PLL (byte_clk_src), halving the byte clock rate.
> > 
> > A simiar issue had been also encountered on SM8750.
> > b8501febdc51 ("clk: qcom: dispcc-sm8750: Drop incorrect CLK_SET_RATE_PARENT on byte intf parent").
> > 
> > Likewise, remove CLK_SET_RATE_PARENT from all four byte divider clocks
> > so that clk_set_rate() on the divider adjusts only the divider ratio,
> > leaving the parent PLL untouched.
> > 
> > Fixes: 4a66e76fdb6d ("clk: qcom: Add SC8280XP display clock controller")
> > Signed-off-by: White Lewis <liu224806@gmail.com>
> > [pengyu: reword]
> > Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
> > ---
> 
> Looks like more platforms have this issue.. thanks for fixing this

I hope within the next week to post a new draft of my patch series to
keep certain clk rates intact when sibling and parent rate changes occur
[1]. This will be for certain critical clks, such as the ones used for
DRM and sound. I have it working with kunit, and just need to clean up
some of my new clk helpers and commit messages before I post a v5.

I'd like to test this on some real hardware and I have the Thinkpad x13s
with the sc8280xp SoC. Can this issue be reproduced on this hardware? If
so, can you provide me detailed instructions about how to trigger this
scenario?

[1] Latest public posting v4 from September
    https://lore.kernel.org/linux-clk/20250923-clk-tests-docs-v4-0-9205cb3d3cba@redhat.com/

Thanks,

Brian