Re: [PATCH 4/5] i2c: qcom-cci: Add OPP table support and enforce FAST_PLUS requirements

Konrad Dybcio
2025-09-08T08:43:58Z

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 <konrad.dybcio@oss.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@oss.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.

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

Konrad