spi: spi-nxp-fspi: limit the clock rate for different sample clock source selection

[ Upstream commit f43579ef3500527649b1c233be7cf633806353aa ]

For different sample clock source selection, the max frequency
flexspi supported are different. For mode 0, max frequency is 66MHz.
For mode 3, the max frequency is 166MHz.

Refer to 3.9.9 FlexSPI timing parameters on page 65.
https://www.nxp.com/docs/en/data-sheet/IMX8MNCEC.pdf

Though flexspi maybe still work under higher frequency, but can't
guarantee the stability. IC suggest to add this limitation on all
SoCs which contain flexspi.

Fixes: c07f27032317 ("spi: spi-nxp-fspi: add the support for sample data from DQS pad")
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Link: https://patch.msgid.link/20250922-fspi-fix-v1-3-ff4315359d31@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/spi/spi-nxp-fspi.c b/drivers/spi/spi-nxp-fspi.c
index bde6d131ab8b73d5d35c560bd8c9b17e641a1317..ab13f11242c3c7718e2d47613a01f3995706417d 100644 (file)
--- a/drivers/spi/spi-nxp-fspi.c
+++ b/drivers/spi/spi-nxp-fspi.c
@@ -404,6 +404,8 @@ struct nxp_fspi {
        int flags;
        /* save the previous operation clock rate */
        unsigned long pre_op_rate;
+       /* the max clock rate fspi output to device */
+       unsigned long max_rate;
 };
 
 static inline int needs_ip_only(struct nxp_fspi *f)
@@ -675,10 +677,13 @@ static void nxp_fspi_select_rx_sample_clk_source(struct nxp_fspi *f,
         * change the mode back to mode 0.
         */
        reg = fspi_readl(f, f->iobase + FSPI_MCR0);
-       if (op_is_dtr)
+       if (op_is_dtr) {
                reg |= FSPI_MCR0_RXCLKSRC(3);
-       else    /*select mode 0 */
+               f->max_rate = 166000000;
+       } else {        /*select mode 0 */
                reg &= ~FSPI_MCR0_RXCLKSRC(3);
+               f->max_rate = 66000000;
+       }
        fspi_writel(f, reg, f->iobase + FSPI_MCR0);
 }
 
@@ -793,6 +798,7 @@ 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);
+       rate = min(f->max_rate, op->max_freq);
 
        if (op_is_dtr) {
                f->flags |= FSPI_DTR_MODE;