Re: [PATCH 4/4] clk: implement sync_state support

[Konrad Dybcio]

On 6/26/26 6:32 PM, Brian Masney wrote:
> The existing support for disabling unused clks runs in the late initcall
> stage, and it has been known for a long time that this is broken since
> it runs too early in the boot up process. It doesn't work for kernel
> modules, and it also doesn't work if all of the consumers haven't fully
> probed yet. Folks have long recommended to boot certain platforms with
> clk_ignore_unused to work around issues with disabling unused clks.

[...]

>     [    0.366737] clk: Disabling unused clocks not associated with a device
>     [    0.367232] PM: genpd: Disabling unused power domains
>     [    7.791413] qcom-qmp-pcie-phy 1c24000.phy: clk: Disabling unused clocks
>     [    7.799702] qcom_aoss_qmp c300000.power-management: clk: Disabling unused clocks
>     [    8.548820] qcom-qmp-pcie-phy 1c14000.phy: clk: Disabling unused clocks
>     [    9.121849] qcom-qmp-usb-phy 88f1000.phy: clk: Disabling unused clocks
>     [    9.121985] qcom-qmp-usb-phy 88ef000.phy: clk: Disabling unused clocks
>     [    9.122691] qcom-edp-phy aec5a00.phy: clk: Disabling unused clocks

Many of these drivers only register fixed "virtual" clocks that
don't lead to any registers being altered and only exist to convey
what the clocks look like on the hw level.. but I don't think we
have great infra to skip that..

>     [    9.122760] disp_cc-sc8280xp af00000.clock-controller: clk: Disabling unused clocks
>     [    9.142121] qcom-qmp-combo-phy 88eb000.phy: clk: Disabling unused clocks
>     [    9.169149] qcom-qmp-combo-phy 8903000.phy: clk: Disabling unused clocks
>     [   16.057997] qcom-cpufreq-hw 18591000.cpufreq: clk: Disabling unused clocks
>     [   16.058149] clk-rpmh 18200000.rsc:clock-controller: clk: Disabling unused clocks
>     [   16.334879] qcom-qmp-pcie-phy 1c06000.phy: clk: Disabling unused clocks
>     [   16.706113] camcc-sc8280xp ad00000.clock-controller: clk: Disabling unused clocks
>     [   21.565731] q6prm-lpass-clock 3000000.remoteproc:glink-edge:gpr:service@2:clock-controller: clk: Disabling unused clocks
>     [   21.597069] va_macro 3370000.codec: clk: Disabling unused clocks
>     [   21.605039] rx_macro 3200000.rxmacro: clk: Disabling unused clocks
>     [   21.630313] wsa_macro 3240000.codec: clk: Disabling unused clocks
>     [   21.635069] tx_macro 3220000.txmacro: clk: Disabling unused clocks

This is a bit noisy, but then it's necessary for debugging the
related hangs. Maybe if it turns out to be a huge issue, we can
hide it behind a _dbg() in the future.

I was hoping/expecting that sync_state would completely replace the
late initcall (which would also simplify this diff), but I'm surprised
to learn that there's a whole bunch of clk_register(dev=NULL)
calls in the kernel (are most of them doing it for no good reason
by chance?)

Konrad