Re: [PATCH RFT v2 01/14] dt-bindings: clock: qcom,rpmcc: Add a way to enable unused clock cleanup

Bjorn Andersson
2023-03-22T03:19:55Z

On Wed, Mar 08, 2023 at 10:35:17PM +0100, Konrad Dybcio wrote:
> Disabling RPMCC clocks can be a bit touchy. If we can't guarantee all
> (or at least most) of the oneline peripherals ask the interconnect
> framework to keep their buses online and guarantee enough bandwidth,
> we're relying on bootloader defaults to keep the said buses alive through
> RPM requests and rate setting on RPM clocks.
>
> Without that in place, the RPM clocks are never enabled in the CCF, which
> qualifies them to be cleaned up, since - as far as Linux is concerned -
> nobody's using them and they're just wasting power. Doing so will end
> tragically, as within miliseconds we'll get *some* access attempt on an
> unlocked bus which will cause a platform crash.
>
> On the other hand, if we want to save power and put well-supported
> platforms to sleep, we should be shutting off at least some of these
> clocks (this time with a clear distinction of which ones are *actually*
> not in use, coming from the interconnect driver).
>
> To differentiate between these two cases while not breaking older DTs,
> introduce an opt-in property to correctly mark RPM clocks as enabled
> after handoff (the initial max freq vote) and hence qualify them for the
> common unused clock cleanup.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
> ---
> Documentation/devicetree/bindings/clock/qcom,rpmcc.yaml | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/clock/qcom,rpmcc.yaml b/Documentation/devicetree/bindings/clock/qcom,rpmcc.yaml
> index 2a95bf8664f9..386153f61971 100644
> --- a/Documentation/devicetree/bindings/clock/qcom,rpmcc.yaml
> +++ b/Documentation/devicetree/bindings/clock/qcom,rpmcc.yaml
> @@ -58,6 +58,12 @@ properties:
> minItems: 1
> maxItems: 2
>
> + qcom,clk-disable-unused:

This is a Linux implementation detail, not a description of the
hardware. So it unfortunately doesn't belong here.

> + type: boolean
> + description:
> + Indicates whether unused RPM clocks can be shut down with the common
> + unused clock cleanup. Requires a functional interconnect driver.

This is an interesting aspect though, there's a lot of things that will
break if any one of these building blocks are missing, for any reason.

Regards,
Bjorn

> +
> required:
> - compatible
> - '#clock-cells'
>
> --
> 2.39.2
>