linux-kernel - Re: [PATCH 4/5] i2c: qcom-cci: Add OPP table support and enforce FAST

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Message-ID: <aL6Vp-3er71AJPJd@linaro.org>
Date: Mon, 8 Sep 2025 10:36:55 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Konrad Dybcio <konradybcio@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	Loic Poulain <loic.poulain@....qualcomm.com>,
	Robert Foss <rfoss@...nel.org>, Andi Shyti <andi.shyti@...nel.org>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH 4/5] i2c: qcom-cci: Add OPP table support and enforce
 FAST_PLUS requirements

On Thu, Sep 04, 2025 at 04:31:23PM +0200, Konrad Dybcio wrote:
> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> 
> The CCI clock has voltage requirements, which need to be described
> through an OPP table.
> 
> The 1 MHz FAST_PLUS mode requires the CCI core clock runs at 37,5 MHz
> (which is a value common across all SoCs), since it's not possible to
> reach the required timings with the default 19.2 MHz rate.
> 
> Address both issues by introducing an OPP table and using it to vote
> for the faster rate.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>

Using an OPP table for a single static rate that remains the same over
the whole lifetime of the driver feels like overkill to me. Couldn't you
just put the "required-opps" directly into the device node so that it is
automatically applied when the device goes in/out of runtime suspend?

And since you need to make DT additions anyway, couldn't you just use
"assigned-clock-rates" to avoid the need for a driver patch entirely? We
use that for e.g. USB clocks as well.

Thanks,
Stephan