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

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Message-ID: <87y0qmenmx.fsf@bootlin.com>
Date: Wed, 10 Sep 2025 10:07:50 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Mark Brown <broonie@...nel.org>
Cc: Santhosh Kumar K <s-k6@...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 14/08/2025 at 13:34:38 +01, Mark Brown <broonie@...nel.org> wrote:

> 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?).

Santhosh, do you need more inputs? Or can you send an updated version?

I am still thinking about the interface on the spi-mem/spi-nand side,
but please iterate so we can move forward.

Thanks,
Miquèl