Re: [PATCH v7 0/8] clk: add support for v1 / v2 clock rate negotiation and kunit tests

[Brian Masney]

On Mon, Mar 23, 2026 at 01:24:51PM -0400, Brian Masney wrote:
> The Common Clock Framework is expected to keep a clock’s rate stable
> after setting a new rate with:
> 
>     clk_set_rate(clk, NEW_RATE);
> 
> Clock consumers do not know about the clock hierarchy, sibling clocks,
> or the type of clocks involved. However, several longstanding issues
> affect how rate changes propagate through the clock tree when
> CLK_SET_RATE_PARENT is involved, and the parent's clock rate is changed:
> 
> - A clock in some cases can unknowingly change a sibling clock's rate.
> 
> - No negotiation is done with the sibling clocks, so an inappropriate
>   or less than ideal parent rate can be selected.
> 
> A selection of some real world examples of where this shows up is at
> [1]. DRM needs to run at precise clock rates, and this issue shows up
> there, however will also show up in other subsystems that require
> precise clock rates, such as sound.
> 
> This series introduces kunit tests to illustrate the current behavior in
> the clk core. As discussed at Linux Plumbers Conference 2025 in Tokyo
> [2], it was suggested to move the negotiation logic into the clk
> providers themselves so that only the clks with this issue can have
> their rate preserved, and add some common helpers to the clk core.

Sashiko identified a few issues with this series, so I'll post a new
version with the fixes.

https://sashiko.dev/#/patchset/20260323-clk-scaling-v7-0-8e7193dc9405%40redhat.com

Brian