spi: spi-fsl-dspi: Enable modified transfer protocol on S32G

S32G supports modified transfer protocol where both host and target
devices sample later in the SCK period than in Classic SPI mode to allow
the logic to tolerate more delays in device pads and board traces. Set
MTFE bit in MCR register for frequencies higher than 25MHz.

Signed-off-by: Andra-Teodora Ilie <andra.ilie@nxp.com>
Signed-off-by: Bogdan-Gabriel Roman <bogdan-gabriel.roman@nxp.com>
Signed-off-by: Larisa Grigore <larisa.grigore@nxp.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Link: https://patch.msgid.link/20250522-james-nxp-spi-v2-11-bea884630cfb@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Andra-Teodora Ilie

drivers/spi/spi-fsl-dspi.c

@@ -24,6 +24,7 @@
 
 #define SPI_MCR				0x00
 #define SPI_MCR_HOST			BIT(31)
+#define SPI_MCR_MTFE			BIT(26)
 #define SPI_MCR_PCSIS(x)		((x) << 16)
 #define SPI_MCR_CLR_TXF			BIT(11)
 #define SPI_MCR_CLR_RXF			BIT(10)
@@ -37,6 +38,7 @@
 
 #define SPI_CTAR(x)			(0x0c + (((x) & GENMASK(2, 0)) * 4))
 #define SPI_CTAR_FMSZ(x)		(((x) << 27) & GENMASK(30, 27))
+#define SPI_CTAR_DBR			BIT(31)
 #define SPI_CTAR_CPOL			BIT(26)
 #define SPI_CTAR_CPHA			BIT(25)
 #define SPI_CTAR_LSBFE			BIT(24)
@@ -111,6 +113,8 @@
 
 #define DMA_COMPLETION_TIMEOUT		msecs_to_jiffies(3000)
 
+#define SPI_25MHZ			25000000
+
 struct chip_data {
 	u32			ctar_val;
 };
@@ -346,6 +350,7 @@ struct fsl_dspi {
 	const void				*tx;
 	void					*rx;
 	u16					tx_cmd;
+	bool					mtf_enabled;
 	const struct fsl_dspi_devtype_data	*devtype_data;
 
 	struct completion			xfer_done;
@@ -722,7 +727,7 @@ static void dspi_release_dma(struct fsl_dspi *dspi)
 }
 
 static void hz_to_spi_baud(char *pbr, char *br, int speed_hz,
-			   unsigned long clkrate)
+			   unsigned long clkrate, bool mtf_enabled)
 {
 	/* Valid baud rate pre-scaler values */
 	int pbr_tbl[4] = {2, 3, 5, 7};
@@ -739,7 +744,13 @@ static void hz_to_spi_baud(char *pbr, char *br, int speed_hz,
 
 	for (i = 0; i < ARRAY_SIZE(brs); i++)
 		for (j = 0; j < ARRAY_SIZE(pbr_tbl); j++) {
-			scale = brs[i] * pbr_tbl[j];
+			if (mtf_enabled) {
+				/* In MTF mode DBR=1 so frequency is doubled */
+				scale = (brs[i] * pbr_tbl[j]) / 2;
+			} else {
+				scale = brs[i] * pbr_tbl[j];
+			}
+
 			if (scale >= scale_needed) {
 				if (scale < minscale) {
 					minscale = scale;
@@ -1146,6 +1157,20 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 	return status;
 }
 
+static int dspi_set_mtf(struct fsl_dspi *dspi)
+{
+	if (spi_controller_is_target(dspi->ctlr))
+		return 0;
+
+	if (dspi->mtf_enabled)
+		regmap_update_bits(dspi->regmap, SPI_MCR, SPI_MCR_MTFE,
+				   SPI_MCR_MTFE);
+	else
+		regmap_update_bits(dspi->regmap, SPI_MCR, SPI_MCR_MTFE, 0);
+
+	return 0;
+}
+
 static int dspi_setup(struct spi_device *spi)
 {
 	struct fsl_dspi *dspi = spi_controller_get_devdata(spi->controller);
@@ -1204,7 +1229,16 @@ static int dspi_setup(struct spi_device *spi)
 		cs_sck_delay, sck_cs_delay);
 
 	clkrate = clk_get_rate(dspi->clk);
-	hz_to_spi_baud(&pbr, &br, spi->max_speed_hz, clkrate);
+
+	if (is_s32g_dspi(dspi) && spi->max_speed_hz > SPI_25MHZ)
+		dspi->mtf_enabled = true;
+	else
+		dspi->mtf_enabled = false;
+
+	dspi_set_mtf(dspi);
+
+	hz_to_spi_baud(&pbr, &br, spi->max_speed_hz, clkrate,
+		       dspi->mtf_enabled);
 
 	/* Set PCS to SCK delay scale values */
 	ns_delay_scale(&pcssck, &cssck, cs_sck_delay, clkrate);
@@ -1226,6 +1260,9 @@ static int dspi_setup(struct spi_device *spi)
 				  SPI_CTAR_PBR(pbr) |
 				  SPI_CTAR_BR(br);
 
+		if (dspi->mtf_enabled)
+			chip->ctar_val |= SPI_CTAR_DBR;
+
 		if (spi->mode & SPI_LSB_FIRST)
 			chip->ctar_val |= SPI_CTAR_LSBFE;
 	}
@@ -1352,6 +1389,8 @@ static int dspi_resume(struct device *dev)
 		return ret;
 	}
 
+	dspi_set_mtf(dspi);
+
 	if (dspi->irq)
 		enable_irq(dspi->irq);