linux-kernel - Re: [RFC PATCH 01/10] spi: spi-mem: Introduce support for tuning controller

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Message-ID: <2f051eae-61c7-4bff-9f85-cf37b02a7ea3@sirena.org.uk>
Date: Thu, 14 Aug 2025 13:34:38 +0100
From: Mark Brown <broonie@...nel.org>
To: Santhosh Kumar K <s-k6@...com>
Cc: miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
	tudor.ambarus@...aro.org, pratyush@...nel.org, mwalle@...nel.org,
	p-mantena@...com, linux-spi@...r.kernel.org,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	a-dutta@...com, u-kumar1@...com, praneeth@...com
Subject: Re: [RFC PATCH 01/10] spi: spi-mem: Introduce support for tuning
 controller

On Thu, Aug 14, 2025 at 05:04:33PM +0530, Santhosh Kumar K wrote:
> On 14/08/25 01:56, Mark Brown wrote:

> > Should we have something that blocks these tuning required modes without
> > the appropriate tuning, and/or allows discovery of which modes require
> > this tuning?  This all feels very landmineish - client drivers just have
> > to know when tuning is required.

> The flash's maximum operating frequency determines whether PHY tuning is
> required, as we need tuning in case of Cadence controller for frequencies
> over 50 MHz.

That's entirely specific to the Candence controller from the sounds of
it, that makes it hard to write a client driver if you need to know
exactly what the controller you're dealing with is and what it's
requirements are.

> And we do check for this condition - see Patch 07/10,
> cqspi_phy_op_eligible_sdr(), which currently verifies the flash frequency
> against 166 MHz. This logic can be improved by implementing both min and max
> frequency checks, will update in the following version.

I can't actually tell how that verifies if the tuning has been done
appropriately TBH, at least not without more effort than I'd care to
(and the tuning only gets added in patch 10?).

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