Re: [RFC PATCH v2 11/12] spi: cadence-quadspi: restrict PHY frequency to tuned operations

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Santhosh Kumar K <s-k6@ti.com>
Cc: <broonie@kernel.org>,  <robh@kernel.org>,  <krzk+dt@kernel.org>,
	<conor+dt@kernel.org>,  <richard@nod.at>,  <vigneshr@ti.com>,
	<tudor.ambarus@linaro.org>,  <pratyush@kernel.org>,
	 <mwalle@kernel.org>, <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>,  <p-mantena@ti.com>, <a-dutta@ti.com>
Subject: Re: [RFC PATCH v2 11/12] spi: cadence-quadspi: restrict PHY frequency to tuned operations
Date: Fri, 13 Feb 2026 09:21:11 +0100	[thread overview]
Message-ID: <874inlxde0.fsf@bootlin.com> (raw)
In-Reply-To: <fdcb19ff-c949-4538-8819-88720e514f04@ti.com> (Santhosh Kumar K.'s message of "Sat, 7 Feb 2026 00:57:04 +0530")

On 07/02/2026 at 00:57:04 +0530, Santhosh Kumar K <s-k6@ti.com> wrote:

> On 05/02/26 23:17, Miquel Raynal wrote:
>> Hi Santhosh,
>> 
>>> +	/*
>>> +	 * PHY tuning allows high-frequency operation only for calibrated
>>> +	 * commands. Uncalibrated operations use safe non-PHY frequency to
>>> +	 * avoid timing violations.
>>> +	 */
>>> +	if (cqspi->ddata->execute_tuning && f_pdata->use_phy &&
>>> +	    (cqspi_op_matches_tuned(op, &f_pdata->phy_read_op) ||
>>> +	     cqspi_op_matches_tuned(op, &f_pdata->phy_write_op))) {
>>> +		cqspi_configure(f_pdata, op->max_freq);
>>> +	} else if (cqspi->ddata->execute_tuning) {
>>> +		/* Use safe frequency for untuned operations */
>>> +		cqspi_configure(f_pdata, f_pdata->non_phy_clk_rate);
>>> +	} else {
>>> +		/* No tuning support, always use requested frequency */
>>> +		cqspi_configure(f_pdata, op->max_freq);
>>> +	}
>> Shouldn't we handle this at the core level? We know what kind of
>> operation pattern we provided, so it is easy to set the correct
>> frequency in the operation structure.
>> Can you please make this happen? Perhaps you can return the operation
>> frequency once the calibration is successful (in the read and write op
>> templates maybe?) so this can be picked up by the core and used for the
>> following operations. This way the controller driver no longer needs to
>> check if the operation has been tuned or not, it can just look at the
>> frequency. When using the highest frequency, PHY tuning must be
>> used/enabled, otherwise not.
>
> No, Miquel, this may not be correct. There can be cases where an
> operation does not require tuning but still can run at maximum
> frequency (166 MHz, for instance).

This is currently not the case. Currently you tune for one or two ops
(read/write) and you enable PHY tuning only on these. Do you plan on
adding such a feature? If not, I would not bother with this now.

> In such scenarios, simply setting
> op->max_freq to the maximum frequency value and deciding whether to
> enable tuning based on an op->max_freq comparison would not be
> sufficient.

If there are such cases, can they be listed? I am sorry but I fail to
see where this would not work. Any examples to share?

Thanks,
Miquèl

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