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

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Date:   Wed, 08 Mar 2023 22:35:17 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        devicetree@...r.kernel.org,
        Konrad Dybcio <konrad.dybcio@...aro.org>
Subject: [PATCH RFT v2 01/14] dt-bindings: clock: qcom,rpmcc: Add a way to
 enable unused clock cleanup

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@...aro.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:
+    type: boolean
+    description:
+      Indicates whether unused RPM clocks can be shut down with the common
+      unused clock cleanup. Requires a functional interconnect driver.
+
 required:
   - compatible
   - '#clock-cells'

-- 
2.39.2