linux-kernel - Re: [RFC PATCH v2 09/12] spi: cadence-quadspi: add PHY tuning infrastructure

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Message-ID: <87bji3gkda.fsf@bootlin.com>
Date: Thu, 05 Feb 2026 18:39:45 +0100
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Santhosh Kumar K <s-k6@...com>
Cc: <broonie@...nel.org>,  <robh@...nel.org>,  <krzk+dt@...nel.org>,
  <conor+dt@...nel.org>,  <richard@....at>,  <vigneshr@...com>,
  <tudor.ambarus@...aro.org>,  <pratyush@...nel.org>,  <mwalle@...nel.org>,
  <linux-spi@...r.kernel.org>,  <devicetree@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>,  <linux-mtd@...ts.infradead.org>,
  <praneeth@...com>,  <u-kumar1@...com>,  <p-mantena@...com>,
  <a-dutta@...com>
Subject: Re: [RFC PATCH v2 09/12] spi: cadence-quadspi: add PHY tuning
 infrastructure

On 13/01/2026 at 19:46:14 +0530, Santhosh Kumar K <s-k6@...com> wrote:

> Implement the spi_controller_mem_ops execute_tuning callback to enable
> PHY tuning support for the Cadence controller. PHY tuning optimizes data
> capture timing at high frequencies by calibrating the read data capture
> delay through the controller's PHY interface.
>
> Tuning algorithm functions (cqspi_phy_tuning_ddr/sdr and
> cqspi_phy_pre/post_config) are placeholders to be implemented
> in subsequent commits.
>
> Signed-off-by: Santhosh Kumar K <s-k6@...com>
> ---
>  drivers/spi/spi-cadence-quadspi.c | 241 ++++++++++++++++++++++++++++++
>  1 file changed, 241 insertions(+)
>
> diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
> index 0df286d24256..b8b0e85f4f68 100644
> --- a/drivers/spi/spi-cadence-quadspi.c
> +++ b/drivers/spi/spi-cadence-quadspi.c
> @@ -32,6 +32,7 @@
>  
>  #define CQSPI_NAME			"cadence-qspi"
>  #define CQSPI_MAX_CHIPSELECT		4
> +#define CQSPI_AM654_NON_PHY_CLK_RATE	25000000
>  
>  static_assert(CQSPI_MAX_CHIPSELECT <= SPI_DEVICE_CS_CNT_MAX);
>  
> @@ -65,6 +66,7 @@ struct cqspi_st;
>  struct cqspi_flash_pdata {
>  	struct cqspi_st	*cqspi;
>  	u32		clk_rate;
> +	u32		non_phy_clk_rate;

This is the second (and last) main issue I have with the series as it is
right now. We cannot set this type of frequency in the driver IMO, it is
too board specific.

We currently have a DT property for the SPI maximum supported
frequency. I believe this is no longer enough. Why not making this
frequency property an array? First frequency would be the default,
non tuned maximum frequency. The second would be the maximum frequency
reachable when tuning the PHY.

The rest of the patch LGTM otherwise, but there is this frequency
information which I think should be handled with more care.

Thanks,
Miquèl