spi: bcm-qspi: Use fastbr setting to allow faster MSPI speeds

Setting MSPI_SPCR3.fastbr=1 allows using clock divider (SPBR) values of
1-7, while the default value prohibits these values and requires a minimum
clock divider value of 8.

Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Link: https://lore.kernel.org/r/20200420190853.45614-8-kdasu.kdev@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bcm-qspi.c

@@ -107,13 +107,15 @@
 #define MSPI_SPCR2_SPE				BIT(6)
 #define MSPI_SPCR2_CONT_AFTER_CMD		BIT(7)
 
+#define MSPI_SPCR3_FASTBR			BIT(0)
+#define MSPI_SPCR3_FASTDT			BIT(1)
+
 #define MSPI_MSPI_STATUS_SPIF			BIT(0)
 
 #define INTR_BASE_BIT_SHIFT			0x02
 #define INTR_COUNT				0x07
 
 #define NUM_CHIPSELECT				4
-#define QSPI_SPBR_MIN				8U
 #define QSPI_SPBR_MAX				255U
 
 #define OPCODE_DIOR				0xBB
@@ -227,6 +229,25 @@ static inline bool has_bspi(struct bcm_qspi *qspi)
 	return qspi->bspi_mode;
 }
 
+/* hardware supports spcr3 and fast baud-rate  */
+static inline bool bcm_qspi_has_fastbr(struct bcm_qspi *qspi)
+{
+	if (!has_bspi(qspi) &&
+	    ((qspi->mspi_maj_rev >= 1) &&
+	     (qspi->mspi_min_rev >= 5)))
+		return true;
+
+	return false;
+}
+
+static inline int bcm_qspi_spbr_min(struct bcm_qspi *qspi)
+{
+	if (bcm_qspi_has_fastbr(qspi))
+		return 1;
+	else
+		return 8;
+}
+
 /* Read qspi controller register*/
 static inline u32 bcm_qspi_read(struct bcm_qspi *qspi, enum base_type type,
 				unsigned int offset)
@@ -534,7 +555,7 @@ static void bcm_qspi_hw_set_parms(struct bcm_qspi *qspi,
 	if (xp->speed_hz)
 		spbr = qspi->base_clk / (2 * xp->speed_hz);
 
-	spcr = clamp_val(spbr, QSPI_SPBR_MIN, QSPI_SPBR_MAX);
+	spcr = clamp_val(spbr, bcm_qspi_spbr_min(qspi), QSPI_SPBR_MAX);
 	bcm_qspi_write(qspi, MSPI, MSPI_SPCR0_LSB, spcr);
 
 	spcr = MSPI_MASTER_BIT;
@@ -544,6 +565,14 @@ static void bcm_qspi_hw_set_parms(struct bcm_qspi *qspi,
 	spcr |= xp->mode & 3;
 	bcm_qspi_write(qspi, MSPI, MSPI_SPCR0_MSB, spcr);
 
+	if (bcm_qspi_has_fastbr(qspi)) {
+		spcr = 0;
+
+		/* enable fastbr */
+		spcr |=	MSPI_SPCR3_FASTBR;
+		bcm_qspi_write(qspi, MSPI, MSPI_SPCR3, spcr);
+	}
+
 	qspi->last_parms = *xp;
 }
 
@@ -1385,7 +1414,6 @@ int bcm_qspi_probe(struct platform_device *pdev,
 	}
 
 	qspi->base_clk = clk_get_rate(qspi->clk);
-	qspi->max_speed_hz = qspi->base_clk / (QSPI_SPBR_MIN * 2);
 
 	if (data->has_mspi_rev) {
 		rev = bcm_qspi_read(qspi, MSPI, MSPI_REV);
@@ -1397,6 +1425,8 @@ int bcm_qspi_probe(struct platform_device *pdev,
 	qspi->mspi_maj_rev = (rev >> 4) & 0xf;
 	qspi->mspi_min_rev = rev & 0xf;
 
+	qspi->max_speed_hz = qspi->base_clk / (bcm_qspi_spbr_min(qspi) * 2);
+
 	bcm_qspi_hw_init(qspi);
 	init_completion(&qspi->mspi_done);
 	init_completion(&qspi->bspi_done);