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

[Conor Dooley]

On Wed, Jun 03, 2026 at 05:54:41PM +0200, Miquel Raynal wrote:
> Hi Conor,
> 
> On 02/06/2026 at 17:18:15 +01, Conor Dooley <conor@xxxxxxxxxx> wrote:
> 
> > On Tue, Jun 02, 2026 at 02:05:53PM +0200, Miquel Raynal wrote:
> >> Hello Conor, Santhosh,
> >> 
> >> >> I also don't get the point of this property, why can't you just set
> >> >> the
> >> >> max that the device can do and if the controller can configure itself to
> >> >> be fast enough it will do so, and if it can't then it'll pick whatever
> >> >> the fastest it can actually do instead?
> >> 
> >> If I may, this is not doable because there is always a phase at low
> >> speed. By low speed, I mean the speed which allows reliable data
> >> transfers between the host and the device. This "maximum low" speed is
> >> non discoverable, it is necessary to describe it. As of today, it is
> >> widely used (and I believe for good reasons) and covers 99.99% of the
> >> use cases.
> >> 
> >> >> Seems like you're abusing a peripheral property to encode information
> >> >> about the controller.
> >> >
> >> > The controller-side approach you mentioned is similar to what I had in
> >> > v2, where a compatible-specific base_freq is used for non-PHY ops.
> >> >
> >> > Miquel,
> >> >
> >> > I think we should revert to the v2 approach.
> >> >
> >> > The non-PHY frequency is a controller limitation/capability rather than
> >> > a flash characteristic, so it seems more appropriate to keep it in the
> >> > controller driver as Conor suggested.
> >> 
> >> The non tuned frequency is the maximum frequency one could use
> >> reliably. It is not controller specific. It is mostly board specific,
> >> and to some extend may also be chip specific.
> >> 
> >> The tuned frequency is the maximum frequency one could use reliably
> >> after line a controller or chip specific training procedure. It is
> >> also the result of an aggregated set of non discoverable hardware
> >> limitations:
> >> - board routing
> >> - chip capability
> >> - controller capability
> >
> > 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.

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