[PATCH] spi: orion: support armada extended baud rates

[gerg@xxxxxxxxxxx]

From: Greg Ungerer <gerg@xxxxxxxxxxx>

The Armada SoC family implementation of this SPI hardware module has
extended the configuration register to allow for a wider range of SPI
clock rates. Specifically the Serial Baud Rate Pre-selection bits in the
SPI Interface Configuration Register now also use bits 6 and 7 as well.

Modify the baud rate calculation to handle these differences for the
Armada case. Potentially a baud rate can be setup using a number of
different pre-scalar and scalar combinations. This code tries all
possible pre-scalar divisors (8 in total) to try and find the most
accuate set.

Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxxx>
---
 drivers/spi/spi-orion.c | 77 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 61 insertions(+), 16 deletions(-)

diff --git a/drivers/spi/spi-orion.c b/drivers/spi/spi-orion.c
index c4675fa..816822f 100644
--- a/drivers/spi/spi-orion.c
+++ b/drivers/spi/spi-orion.c
@@ -40,6 +40,7 @@
 #define ORION_SPI_MODE_CPHA		(1 << 12)
 #define ORION_SPI_IF_8_16_BIT_MODE	(1 << 5)
 #define ORION_SPI_CLK_PRESCALE_MASK	0x1F
+#define ARMADA_SPI_CLK_PRESCALE_MASK	0xDF
 #define ORION_SPI_MODE_MASK		(ORION_SPI_MODE_CPOL | \
 					 ORION_SPI_MODE_CPHA)
 
@@ -82,31 +83,74 @@ static int orion_spi_baudrate_set(struct spi_device *spi, unsigned int speed)
 	u32 rate;
 	u32 prescale;
 	u32 reg;
+	u32 mask;
 	struct orion_spi *orion_spi;
 
 	orion_spi = spi_master_get_devdata(spi->master);
 
 	tclk_hz = clk_get_rate(orion_spi->clk);
 
-	/*
-	 * the supported rates are: 4,6,8...30
-	 * round up as we look for equal or less speed
-	 */
-	rate = DIV_ROUND_UP(tclk_hz, speed);
-	rate = roundup(rate, 2);
+	if (of_machine_is_compatible("marvell,armada370")) {
+		unsigned int clk, spr, sppr, sppr2, err;
+		unsigned int best_spr, best_sppr, best_err;
 
-	/* check if requested speed is too small */
-	if (rate > 30)
-		return -EINVAL;
+		best_err = speed;
+		best_spr = 0;
+		best_sppr = 0;
 
-	if (rate < 4)
-		rate = 4;
+		tclk_hz *= 10;
+		if (speed > tclk_hz)
+			return -EINVAL;
 
-	/* Convert the rate to SPI clock divisor value.	*/
-	prescale = 0x10 + rate/2;
+		/* Iterate over the valid range looking for best fit */
+		for (sppr = 0; sppr < 8; sppr++) {
+			sppr2 = 0x1 << sppr;
+
+			spr = tclk_hz / sppr2;
+			spr = DIV_ROUND_UP(spr, speed);
+			if ((spr == 0) || (spr > 15))
+				continue;
+
+			clk = tclk_hz / (spr * sppr2);
+			err = speed - clk;
+
+			if (err < best_err) {
+				best_spr = spr;
+				best_sppr = sppr;
+				best_err = err;
+			}
+		}
+
+		if ((best_sppr == 0) && (best_spr == 0))
+			return -EINVAL;
+
+		prescale = ((best_sppr & 0x6) << 5) |
+			((best_sppr & 0x1) << 4) | best_spr;
+
+		mask = ARMADA_SPI_CLK_PRESCALE_MASK;
+	} else {
+		mask = ORION_SPI_CLK_PRESCALE_MASK;
+
+		/*
+		 * the supported rates are: 4,6,8...30
+		 * round up as we look for equal or less speed
+		 */
+		rate = DIV_ROUND_UP(tclk_hz, speed);
+		rate = roundup(rate, 2);
+
+		/* check if requested speed is too small */
+		if (rate > 30)
+			return -EINVAL;
+
+		if (rate < 4)
+			rate = 4;
+
+		/* Convert the rate to SPI clock divisor value.	*/
+		prescale = 0x10 + rate/2;
+	}
 
 	reg = readl(spi_reg(orion_spi, ORION_SPI_IF_CONFIG_REG));
-	reg = ((reg & ~ORION_SPI_CLK_PRESCALE_MASK) | prescale);
+	reg = ((reg & ~mask) | prescale);
 	writel(reg, spi_reg(orion_spi, ORION_SPI_IF_CONFIG_REG));
 
 	return 0;
@@ -348,7 +392,7 @@ static int orion_spi_probe(struct platform_device *pdev)
 	struct orion_spi *spi;
 	struct resource *r;
 	unsigned long tclk_hz;
-	int status = 0;
+	int mindiv, status = 0;
 
 	master = spi_alloc_master(&pdev->dev, sizeof(*spi));
 	if (master == NULL) {
@@ -390,7 +434,8 @@ static int orion_spi_probe(struct platform_device *pdev)
 
 	tclk_hz = clk_get_rate(spi->clk);
 	master->max_speed_hz = DIV_ROUND_UP(tclk_hz, 4);
-	master->min_speed_hz = DIV_ROUND_UP(tclk_hz, 30);
+	mindiv = (of_machine_is_compatible("marvell,armada370")) ? 1920 : 30;
+	master->min_speed_hz = DIV_ROUND_UP(tclk_hz, mindiv);
 
 	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	spi->base = devm_ioremap_resource(&pdev->dev, r);
-- 
1.9.1

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