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

On Mon, Sep 08, 2025 at 10:43:50AM +0200, Konrad Dybcio wrote:

On 9/8/25 10:36 AM, Stephan Gerhold wrote:

quoted

On Thu, Sep 04, 2025 at 04:31:23PM +0200, Konrad Dybcio wrote:

quoted

From: Konrad Dybcio <redacted>

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 <redacted>

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