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

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Message-ID: <20487e7f-33dd-4b65-b1a8-5bb8a06ef859@ti.com>
Date: Thu, 14 Aug 2025 17:04:33 +0530
From: Santhosh Kumar K <s-k6@...com>
To: Mark Brown <broonie@...nel.org>
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>, <s-k6@...com>
Subject: Re: [RFC PATCH 01/10] spi: spi-mem: Introduce support for tuning
 controller

Hello Mark,

On 14/08/25 01:56, Mark Brown wrote:
> On Tue, Aug 12, 2025 at 01:02:10AM +0530, Santhosh Kumar K wrote:
>> From: Pratyush Yadav <pratyush@...nel.org>
>>
>> Some controllers like the Cadence OSPI controller need to perform a
>> tuning sequence to operate at high data rates. Tuning is needs to happen
>> once the device is switched to appropriate mode (say 8S-8S-8S or
>> 8D-8D-8D). Add a hook that spi-mem client devices can call in order to tune
>> the controller to operate in a given mode and data rate.
>>
>> This is somewhat similar to eMMC/SD tuning for higher speed modes like
>> HS200, but there isn't a standard specification around the same though.
> 
> 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.

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.

Thanks,
Santhosh.