linux-kernel - Re: [PATCH 3/5] spi: spi-nxp-fspi: add the support for sample data from DQS pad

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Message-ID: <aMmEMQoa4LMBtkYI@lizhi-Precision-Tower-5810>
Date: Tue, 16 Sep 2025 11:37:21 -0400
From: Frank Li <Frank.li@....com>
To: Haibo Chen <haibo.chen@....com>
Cc: Han Xu <han.xu@....com>, Yogesh Gaur <yogeshgaur.83@...il.com>,
	Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
	imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] spi: spi-nxp-fspi: add the support for sample data
 from DQS pad

On Tue, Sep 16, 2025 at 03:56:42PM +0800, Haibo Chen wrote:
> flexspi define four mode for sample clock source selection.
> Here is the list of modes:
> mode 0: Dummy Read strobe generated by FlexSPI Controller and loopback
>         internally
> mode 1: Dummy Read strobe generated by FlexSPI Controller and loopback
>         from DQS pad
> mode 2: Reserved
> mode 3: Flash provided Read strobe and input from DQS pad
>
> In default, flexspi use mode 0 after reset. And for DTR mode, flexspi
> only support 8D-8D-8D mode. For 8D-8D-8D mode, IC suggest to use mode 3,
> otherwise read always get incorrect data.
>
> Signed-off-by: Haibo Chen <haibo.chen@....com>
> ---
>  drivers/spi/spi-nxp-fspi.c | 52 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 50 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/spi/spi-nxp-fspi.c b/drivers/spi/spi-nxp-fspi.c
> index 6b3e6b427ba84734a2359a964635a8f05cd146fd..be1e56072b94f38af934556055e321d9834bb07b 100644
> --- a/drivers/spi/spi-nxp-fspi.c
> +++ b/drivers/spi/spi-nxp-fspi.c
> @@ -400,6 +400,7 @@ struct nxp_fspi {
>  	struct pm_qos_request pm_qos_req;
>  	int selected;
>  #define FSPI_NEED_INIT		(1 << 0)
> +#define FSPI_DTR_MODE		(1 << 1)

Can you change to use BIT(1)

Frank
>  	int flags;
>  };
>
> @@ -657,6 +658,43 @@ static void nxp_fspi_clk_disable_unprep(struct nxp_fspi *f)
>  	return;
>  }
>
> +/*
> + * Sample Clock source selection for Flash Reading
> + * Four modes defined by fspi:
> + * mode 0: Dummy Read strobe generated by FlexSPI Controller
> + *         and loopback internally
> + * mode 1: Dummy Read strobe generated by FlexSPI Controller
> + *         and loopback from DQS pad
> + * mode 2: Reserved
> + * mode 3: Flash provided Read strobe and input from DQS pad
> + *
> + * fspi default use mode 0 after reset
> + */
> +static void nxp_fspi_select_rx_sample_clk_source(struct nxp_fspi *f,
> +						 bool op_is_dtr)
> +{
> +	u32 reg;
> +
> +	/*
> +	 * For 8D-8D-8D mode, need to use mode 3 (Flash provided Read
> +	 * strobe and input from DQS pad), otherwise read operaton may
> +	 * meet issue.
> +	 * This mode require flash device connect the DQS pad on board.
> +	 * For other modes, still use mode 0, keep align with before.
> +	 * spi_nor_suspend will disable 8D-8D-8D mode, also need to
> +	 * change the mode back to mode 0.
> +	 */
> +	if (op_is_dtr) {
> +		reg = fspi_readl(f, f->iobase + FSPI_MCR0);
> +		reg |= FSPI_MCR0_RXCLKSRC(3);
> +		fspi_writel(f, reg, f->iobase + FSPI_MCR0);
> +	} else {
> +		reg = fspi_readl(f, f->iobase + FSPI_MCR0);
> +		reg &= ~FSPI_MCR0_RXCLKSRC(3);	/* select mode 0 */
> +		fspi_writel(f, reg, f->iobase + FSPI_MCR0);
> +	}


	reg = fspi_readl(f, f->iobase + FSPI_MCR0);
	if (op_is_dtr)
		reg |= FSPI_MCR0_RXCLKSRC(3);
	else
		reg &= ~FSPI_MCR0_RXCLKSRC(3);  /* select mode 0 */
	fspi_writel(f, reg, f->iobase + FSPI_MCR0);

Is it better?

Frank
> +}
> +
>  static void nxp_fspi_dll_calibration(struct nxp_fspi *f)
>  {
>  	int ret;
> @@ -738,15 +776,18 @@ static void nxp_fspi_dll_override(struct nxp_fspi *f)
>  static void nxp_fspi_select_mem(struct nxp_fspi *f, struct spi_device *spi,
>  				const struct spi_mem_op *op)
>  {
> +	/* flexspi only support one DTR mode: 8D-8D-8D */
> +	bool op_is_dtr = op->cmd.dtr && op->addr.dtr && op->dummy.dtr && op->data.dtr;
>  	unsigned long rate = op->max_freq;
>  	int ret;
>  	uint64_t size_kb;
>
>  	/*
>  	 * Return, if previously selected target device is same as current
> -	 * requested target device.
> +	 * requested target device. Also the DTR or STR mode do not change.
>  	 */
> -	if (f->selected == spi_get_chipselect(spi, 0))
> +	if ((f->selected == spi_get_chipselect(spi, 0)) &&
> +	    (!!(f->flags & FSPI_DTR_MODE) == op_is_dtr))
>  		return;
>
>  	/* Reset FLSHxxCR0 registers */
> @@ -763,6 +804,13 @@ static void nxp_fspi_select_mem(struct nxp_fspi *f, struct spi_device *spi,
>
>  	dev_dbg(f->dev, "Target device [CS:%x] selected\n", spi_get_chipselect(spi, 0));
>
> +	nxp_fspi_select_rx_sample_clk_source(f, op_is_dtr);
> +
> +	if (op_is_dtr)
> +		f->flags |= FSPI_DTR_MODE;
> +	else
> +		f->flags &= ~FSPI_DTR_MODE;
> +
>  	nxp_fspi_clk_disable_unprep(f);
>
>  	ret = clk_set_rate(f->clk, rate);
>
> --
> 2.34.1
>