Re: [PATCH v3 01/13] spi: dt-bindings: allow spi-max-frequency to specify a frequency pair

[Conor Dooley]

On Thu, Jun 04, 2026 at 09:14:16AM +0200, Miquel Raynal wrote:
> Hi Conor,
> 
> >> >> > Right, and this I guess is what scuppers letting the controller driver
> >> >> > sort the configuration out itself and leaving the property as-is.
> >> >> > It could be that the speed in spi-max-frequency is lower than the "base
> >> >> > speed" of the controller but because of board routing or device
> >> >> > capability that the tuned mode is still required, right?
> >> >> 
> >> >> I do not actually expect any tuned mode/frequency to be mandatory.
> >> >
> >> > I think you misunderstood my use of "required", I meant that the new
> >> > property/information was needed in the scenario I described, not that it
> >> > should be a required property in a binding.
> >> 
> >> Yes I misunderstood the term indeed. However I still fail to catch what
> >> you meant here, I'm sorry. Would you mind rephrasing?
> >
> > I was talking about a scenario where you want to use the tuned mode to
> > achieve the maximum rate because of the device and/or board configuration,
> > but the rate is below the point where the controller would need tuning.
> > Say the controller needs tuning above 8 Hz but the conditions require
> > tuning to achieve more than 5 Hz. In this example, if the device can do
> > 6 Hz, spi-max-frequency (in the current form) would be set to 6 Hz, and
> > the controller would not enable the tuned mode, leading to problems
> > because the inflection point determined from the controller compatible
> > of 8 Hz would not have been reached.
> 
> I don't think this is a real situation. If the "conditions", as you say
> (ie. PCB routing, mostly) require tuning above 5, then spi-max-frequency
> should be 5.

Then tuning mode would never be used. Remember, this is a theoretical world
where spi-max-frequency would contain the tuned frequency and the
controller was using compatible-specific speed thresholds to determine
if tuning was required.

> It is the frequency that is reachable without any
> tuning. Tuning is just a plus. If tuning fails, we fallback to the
> regular "base" speed, which just works.
> 
> Thanks,
> Miquèl

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