spi: spi-nxp-fspi: add the support for sample data from DQS pad

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.

For DTR mode, flexspi will automatically div 2 of the root clock
and output to device. the formula is:
    device_clock = root_clock / (is_dtr ? 2 : 1)
So correct the clock rate setting for DTR mode to get the max
performance.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250917-flexspi-ddr-v2-4-bb9fe2a01889@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-nxp-fspi.c b/drivers/spi/spi-nxp-fspi.c
index bd61f951d6befdb78cdd84d4531aab378a47c56f..d25679fafad7a94a7ea2a79d7e3da53f4939c9fa 100644 (file)
--- a/drivers/spi/spi-nxp-fspi.c
+++ b/drivers/spi/spi-nxp-fspi.c
@@ -399,7 +399,8 @@ struct nxp_fspi {
        struct mutex lock;
        struct pm_qos_request pm_qos_req;
        int selected;
-#define FSPI_NEED_INIT         (1 << 0)
+#define FSPI_NEED_INIT         BIT(0)
+#define FSPI_DTR_MODE          BIT(1)
        int flags;
 };
 
@@ -655,6 +656,40 @@ 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.
+        */
+       reg = fspi_readl(f, f->iobase + FSPI_MCR0);
+       if (op_is_dtr)
+               reg |= FSPI_MCR0_RXCLKSRC(3);
+       else    /*select mode 0 */
+               reg &= ~FSPI_MCR0_RXCLKSRC(3);
+       fspi_writel(f, reg, f->iobase + FSPI_MCR0);
+}
+
 static void nxp_fspi_dll_calibration(struct nxp_fspi *f)
 {
        int ret;
@@ -736,15 +771,18 @@ 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 */
@@ -761,6 +799,18 @@ 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;
+               /* For DTR mode, flexspi will default div 2 and output to device.
+                * so here to config the root clock to 2 * device rate.
+                */
+               rate = rate * 2;
+       } else {
+               f->flags &= ~FSPI_DTR_MODE;
+       }
+
        nxp_fspi_clk_disable_unprep(f);
 
        ret = clk_set_rate(f->clk, rate);