[PATCH 0/2] spi: fsl-dspi (vf610) clock fixes

[PATCH 0/2] spi: fsl-dspi (vf610) clock fixes

[Aaron Brice]

We were having intermittent problems writing to SRAM chip on SPI bus on vf610
SoM.  Added support for CS setup and hold times to meet the SRAM spec.  In the
process noticed that the baud rate was a little high.

Aaron Brice (2):
  spi: fsl-dspi: Fix clock rate scale values
  spi: fsl-dspi: Add ~50ns delay between cs and sck

 drivers/spi/spi-fsl-dspi.c | 84 ++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 70 insertions(+), 14 deletions(-)

-- 
2.1.0

[PATCH 1/2] spi: fsl-dspi: Fix clock rate scale values

[Aaron Brice]

Update baud rate scaling algorithm to get better scaling values.

Signed-off-by: Aaron Brice <aaron.brice-vSOi0k5x9wFWk0Htik3J/w@public.gmane.org>
---
 drivers/spi/spi-fsl-dspi.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index d1a3924..96cac87 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -148,23 +148,30 @@ static void hz_to_spi_baud(char *pbr, char *br, int speed_hz,
 		16,	32,	64,	128,
 		256,	512,	1024,	2048,
 		4096,	8192,	16384,	32768 };
-	int temp, i = 0, j = 0;
-
-	temp = clkrate / 2 / speed_hz;
-
-	for (i = 0; i < ARRAY_SIZE(pbr_tbl); i++)
-		for (j = 0; j < ARRAY_SIZE(brs); j++) {
-			if (pbr_tbl[i] * brs[j] >= temp) {
-				*pbr = i;
-				*br = j;
-				return;
+	int scale_needed, scale, minscale = INT_MAX;
+	int i, j;
+
+	scale_needed = clkrate / 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 (scale >= scale_needed) {
+				if (scale < minscale) {
+					minscale = scale;
+					*br = i;
+					*pbr = j;
+				}
+				break;
 			}
 		}
 
-	pr_warn("Can not find valid baud rate,speed_hz is %d,clkrate is %ld\
-		,we use the max prescaler value.\n", speed_hz, clkrate);
-	*pbr = ARRAY_SIZE(pbr_tbl) - 1;
-	*br =  ARRAY_SIZE(brs) - 1;
+	if (minscale == INT_MAX) {
+		pr_warn("Can not find valid baud rate,speed_hz is %d,clkrate is %ld, we use the max prescaler value.\n",
+			speed_hz, clkrate);
+		*pbr = ARRAY_SIZE(pbr_tbl) - 1;
+		*br =  ARRAY_SIZE(brs) - 1;
+	}
 }
 
 static int dspi_transfer_write(struct fsl_dspi *dspi)
-- 
2.1.0

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Re: [PATCH 1/2] spi: fsl-dspi: Fix clock rate scale values

[Mark Brown]

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On Fri, Mar 27, 2015 at 02:51:42PM -0700, Aaron Brice wrote:
> Update baud rate scaling algorithm to get better scaling values.

Can we have a better changelog please?  What is better about the new
algorithm?

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[PATCH 2/2] spi: fsl-dspi: Add ~50ns delay between cs and sck

[Aaron Brice]

Add delay between chip select and clock signals, before clock starts and
after clock stops.

Signed-off-by: Aaron Brice <aaron.brice@datasoft.com>
---
 drivers/spi/spi-fsl-dspi.c | 53 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index 96cac87..41284cc 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -20,6 +20,7 @@
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
+#include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
@@ -51,7 +52,7 @@
 #define SPI_CTAR_CPOL(x)	((x) << 26)
 #define SPI_CTAR_CPHA(x)	((x) << 25)
 #define SPI_CTAR_LSBFE(x)	((x) << 24)
-#define SPI_CTAR_PCSSCR(x)	(((x) & 0x00000003) << 22)
+#define SPI_CTAR_PCSSCK(x)	(((x) & 0x00000003) << 22)
 #define SPI_CTAR_PASC(x)	(((x) & 0x00000003) << 20)
 #define SPI_CTAR_PDT(x)	(((x) & 0x00000003) << 18)
 #define SPI_CTAR_PBR(x)	(((x) & 0x00000003) << 16)
@@ -59,6 +60,7 @@
 #define SPI_CTAR_ASC(x)	(((x) & 0x0000000f) << 8)
 #define SPI_CTAR_DT(x)		(((x) & 0x0000000f) << 4)
 #define SPI_CTAR_BR(x)		((x) & 0x0000000f)
+#define SPI_CTAR_SCALE_BITS	0xf
 
 #define SPI_CTAR0_SLAVE	0x0c
 
@@ -99,6 +101,8 @@
 #define SPI_CS_ASSERT		0x02
 #define SPI_CS_DROP		0x04
 
+#define NSEC_PER_SEC		1000000000L
+
 struct chip_data {
 	u32 mcr_val;
 	u32 ctar_val;
@@ -174,6 +178,40 @@ static void hz_to_spi_baud(char *pbr, char *br, int speed_hz,
 	}
 }
 
+static void ns_delay_scale(char *psc, char *sc, int delay_ns,
+		unsigned long clkrate)
+{
+	int pscale_tbl[4] = {1, 3, 5, 7};
+	int scale_needed, scale, minscale = INT_MAX;
+	int i, j;
+	u32 remainder;
+
+	scale_needed = div_u64_rem((u64)delay_ns * clkrate, NSEC_PER_SEC,
+			&remainder);
+	if (remainder)
+		scale_needed++;
+
+	for (i = 0; i < ARRAY_SIZE(pscale_tbl); i++)
+		for (j = 0; j <= SPI_CTAR_SCALE_BITS; j++) {
+			scale = pscale_tbl[i] * (2 << j);
+			if (scale >= scale_needed) {
+				if (scale < minscale) {
+					minscale = scale;
+					*psc = i;
+					*sc = j;
+				}
+				break;
+			}
+		}
+
+	if (minscale == INT_MAX) {
+		pr_warn("Cannot find correct scale values for %dns delay at clkrate %ld, using max prescaler value",
+			delay_ns, clkrate);
+		*psc = ARRAY_SIZE(pscale_tbl) - 1;
+		*sc = SPI_CTAR_SCALE_BITS;
+	}
+}
+
 static int dspi_transfer_write(struct fsl_dspi *dspi)
 {
 	int tx_count = 0;
@@ -352,7 +390,8 @@ static int dspi_setup(struct spi_device *spi)
 {
 	struct chip_data *chip;
 	struct fsl_dspi *dspi = spi_master_get_devdata(spi->master);
-	unsigned char br = 0, pbr = 0, fmsz = 0;
+	unsigned char br = 0, pbr = 0, pcssck = 0, cssck = 0;
+	unsigned char pasc = 0, asc = 0, fmsz = 0;
 
 	if ((spi->bits_per_word >= 4) && (spi->bits_per_word <= 16)) {
 		fmsz = spi->bits_per_word - 1;
@@ -377,10 +416,20 @@ static int dspi_setup(struct spi_device *spi)
 	hz_to_spi_baud(&pbr, &br,
 			spi->max_speed_hz, clk_get_rate(dspi->clk));
 
+	/* Set PCS to SCK delay scale values for 50ns delay*/
+	ns_delay_scale(&pcssck, &cssck, 50, clk_get_rate(dspi->clk));
+
+	/* Set After SCK delay scale values for 50ns delay*/
+	ns_delay_scale(&pasc, &asc, 50, clk_get_rate(dspi->clk));
+
 	chip->ctar_val =  SPI_CTAR_FMSZ(fmsz)
 		| SPI_CTAR_CPOL(spi->mode & SPI_CPOL ? 1 : 0)
 		| SPI_CTAR_CPHA(spi->mode & SPI_CPHA ? 1 : 0)
 		| SPI_CTAR_LSBFE(spi->mode & SPI_LSB_FIRST ? 1 : 0)
+		| SPI_CTAR_PCSSCK(pcssck)
+		| SPI_CTAR_CSSCK(cssck)
+		| SPI_CTAR_PASC(pasc)
+		| SPI_CTAR_ASC(asc)
 		| SPI_CTAR_PBR(pbr)
 		| SPI_CTAR_BR(br);
 
-- 
2.1.0