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Mon, 08 Sep 2025 01:46:53 -0700 (PDT) Date: Mon, 8 Sep 2025 10:46:49 +0200 From: Stephan Gerhold To: Konrad Dybcio Cc: Konrad Dybcio , Bjorn Andersson , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Bryan O'Donoghue , Loic Poulain , Robert Foss , Andi Shyti , Marijn Suijten , linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org Subject: Re: [PATCH 4/5] i2c: qcom-cci: Add OPP table support and enforce FAST_PLUS requirements Message-ID: References: <20250904-topic-cci_updates-v1-0-d38559692703@oss.qualcomm.com> <20250904-topic-cci_updates-v1-4-d38559692703@oss.qualcomm.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Sep 08, 2025 at 10:43:50AM +0200, Konrad Dybcio wrote: > On 9/8/25 10:36 AM, Stephan Gerhold wrote: > > On Thu, Sep 04, 2025 at 04:31:23PM +0200, Konrad Dybcio wrote: > >> From: Konrad Dybcio > >> > >> 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 > > > > 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. > > This is futureproofing, in case someone invents FastMode++ with a higher > dvfs requirement or for when the driver adds presets for a 19.2 MHz CCI > clock which would (marginally) decrease power consumption > If 19.2 MHz CCI clock is feasible and has lower voltage requirements, then I would expect a separate entry for 19.2 MHz in the OPP table of PATCH 5/5? The DT is unrelated to what functionality you implement in the driver, and that would make the OPP table look less useless. :-) Thanks, Stephan