spi: fsl-dspi: Add ~50ns delay between cs and sck

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

Signed-off-by: Aaron Brice <aaron.brice@datasoft.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 60 insertions, 4 deletions

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index 96cac87c9f85..4b6032dd0990 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>
@@ -29,6 +30,7 @@
 #include <linux/sched.h>
 #include <linux/spi/spi.h>
 #include <linux/spi/spi_bitbang.h>
+#include <linux/time.h>
 
 #define DRIVER_NAME "fsl-dspi"
 
@@ -51,7 +53,7 @@
 #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 +61,7 @@
 #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
 
@@ -174,6 +177,40 @@ 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 +389,10 @@ 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;
+        u32 cs_sck_delay = 0, sck_cs_delay = 0;
+        unsigned char br = 0, pbr = 0, pcssck = 0, cssck = 0;
+        unsigned char pasc = 0, asc = 0, fmsz = 0;
+        unsigned long clkrate;
 
         if ((spi->bits_per_word >= 4) && (spi->bits_per_word <= 16)) {
                 fmsz = spi->bits_per_word - 1;
@@ -369,18 +409,34 @@ static int dspi_setup(struct spi_device *spi)
                         return -ENOMEM;
         }
 
+        of_property_read_u32(spi->dev.of_node, "fsl,spi-cs-sck-delay",
+                        &cs_sck_delay);
+
+        of_property_read_u32(spi->dev.of_node, "fsl,spi-sck-cs-delay",
+                        &sck_cs_delay);
+
         chip->mcr_val = SPI_MCR_MASTER | SPI_MCR_PCSIS |
                 SPI_MCR_CLR_TXF | SPI_MCR_CLR_RXF;
 
         chip->void_write_data = 0;
 
-        hz_to_spi_baud(&pbr, &br,
-                        spi->max_speed_hz, clk_get_rate(dspi->clk));
+        clkrate = clk_get_rate(dspi->clk);
+        hz_to_spi_baud(&pbr, &br, spi->max_speed_hz, clkrate);
+
+        /* Set PCS to SCK delay scale values */
+        ns_delay_scale(&pcssck, &cssck, cs_sck_delay, clkrate);
+
+        /* Set After SCK delay scale values */
+        ns_delay_scale(&pasc, &asc, sck_cs_delay, clkrate);
 
         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);