Re: [PATCH v2 2/3] spi: spi-nxp-fspi: enter stop mode before reconfiguring MCR0 and DLL

[Frank Li <Frank.li@oss.nxp.com>]

On Tue, Jul 28, 2026 at 06:18:09PM +0800, haibo.chen@oss.nxp.com wrote:
> From: Haibo Chen <haibo.chen@nxp.com>
>
> In nxp_fspi_select_mem() the RX sample clock source (MCR0[RXCLKSRC])
> and the DLL control registers (DLLxCR) are reconfigured while the
> FlexSPI module is still enabled. According to the FlexSPI reference
> manual initialization sequence, MCR0 and the DLL control registers
> should be programmed while the module is in stop mode, i.e. with
> MCR0[MDIS] set to 1, and the module re-enabled (MCR0[MDIS] = 0)
> afterwards.
>
> Wrap the RX sample clock source selection and the DLL calibration/
> override reconfiguration in a stop-mode window to align with the RM
> and avoid reconfiguring timing-critical registers while the module is
> active.
>
> Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
> ---

Reviewed-by: Frank Li <Frank.Li@nxp.com>

>  drivers/spi/spi-nxp-fspi.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/drivers/spi/spi-nxp-fspi.c b/drivers/spi/spi-nxp-fspi.c
> index 6de6d432cdcb2ee383a02d72f20000045903e176..a426b8d92193a4e303f411cd17c16cb31c3f3873 100644
> --- a/drivers/spi/spi-nxp-fspi.c
> +++ b/drivers/spi/spi-nxp-fspi.c
> @@ -867,6 +867,7 @@ static void nxp_fspi_select_mem(struct nxp_fspi *f, struct spi_device *spi,
>  	unsigned long rate = op->max_freq;
>  	int ret;
>  	uint64_t size_kb;
> +	u32 reg;
>
>  	/*
>  	 * Return when following condition all meet,
> @@ -896,6 +897,15 @@ 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));
>
> +	/*
> +	 * Per the FlexSPI reference manual (initialization sequence), MCR0 and
> +	 * the DLL control registers should be configured while the module is in
> +	 * stop mode (MCR0[MDIS] = 1). Enter stop mode before reconfiguring the
> +	 * RX sample clock source and the DLL, then exit stop mode afterwards.
> +	 */
> +	reg = fspi_readl(f, f->iobase + FSPI_MCR0);
> +	fspi_writel(f, reg | FSPI_MCR0_MDIS, f->iobase + FSPI_MCR0);
> +
>  	nxp_fspi_select_rx_sample_clk_source(f, op_is_dtr);
>  	rate = min(f->max_rate, op->max_freq);
>
> @@ -928,6 +938,10 @@ static void nxp_fspi_select_mem(struct nxp_fspi *f, struct spi_device *spi,
>  	else
>  		nxp_fspi_dll_override(f);
>
> +	/* Exit stop mode now that MCR0 and the DLL have been reconfigured. */
> +	reg = fspi_readl(f, f->iobase + FSPI_MCR0);
> +	fspi_writel(f, reg & ~FSPI_MCR0_MDIS, f->iobase + FSPI_MCR0);
> +
>  	f->pre_op_rate = op->max_freq;
>
>  	f->selected = spi_get_chipselect(spi, 0);
>
> --
> 2.34.1
>
>