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

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Conor Dooley <conor@kernel.org>
Cc: Santhosh Kumar K <s-k6@ti.com>,
	 broonie@kernel.org,  robh@kernel.org, krzk+dt@kernel.org,
	 conor+dt@kernel.org,  richard@nod.at, vigneshr@ti.com,
	 pratyush@kernel.org,  mwalle@kernel.org,
	takahiro.kuwano@infineon.com,  linux-spi@vger.kernel.org,
	devicetree@vger.kernel.org,  linux-kernel@vger.kernel.org,
	linux-mtd@lists.infradead.org,  praneeth@ti.com,
	 u-kumar1@ti.com, a-dutta@ti.com
Subject: Re: [PATCH v3 01/13] spi: dt-bindings: allow spi-max-frequency to specify a frequency pair
Date: Thu, 04 Jun 2026 09:14:16 +0200	[thread overview]
Message-ID: <87ik7yydyv.fsf@bootlin.com> (raw)
In-Reply-To: <20260603-balance-encounter-94f69e1577f3@spud> (Conor Dooley's message of "Wed, 3 Jun 2026 17:40:15 +0100")

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. 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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