SPI: spi_txx9: Fix bit rate calculation

TXx9 SPI bit rate is calculated by:
        fBR = (spi-baseclk) / (n + 1)
Fix calculation of min_speed_hz, max_speed_hz and n.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/drivers/spi/spi_txx9.c b/drivers/spi/spi_txx9.c
index 96057de133ad..19f75627c3de 100644
--- a/drivers/spi/spi_txx9.c
+++ b/drivers/spi/spi_txx9.c
@@ -29,6 +29,8 @@
 
 
 #define SPI_FIFO_SIZE 4
+#define SPI_MAX_DIVIDER 0xff    /* Max. value for SPCR1.SER */
+#define SPI_MIN_DIVIDER 1       /* Min. value for SPCR1.SER */
 
 #define TXx9_SPMCR              0x00
 #define TXx9_SPCR0              0x04
@@ -193,11 +195,8 @@ static void txx9spi_work_one(struct txx9spi *c, struct spi_message *m)
 
                 if (prev_speed_hz != speed_hz
                                 || prev_bits_per_word != bits_per_word) {
-                        u32 n = (c->baseclk + speed_hz - 1) / speed_hz;
-                        if (n < 1)
-                                n = 1;
-                        else if (n > 0xff)
-                                n = 0xff;
+                        int n = DIV_ROUND_UP(c->baseclk, speed_hz) - 1;
+                        n = clamp(n, SPI_MIN_DIVIDER, SPI_MAX_DIVIDER);
                         /* enter config mode */
                         txx9spi_wr(c, mcr | TXx9_SPMCR_CONFIG | TXx9_SPMCR_BCLR,
                                         TXx9_SPMCR);
@@ -370,8 +369,8 @@ static int __init txx9spi_probe(struct platform_device *dev)
                 goto exit;
         }
         c->baseclk = clk_get_rate(c->clk);
-        c->min_speed_hz = (c->baseclk + 0xff - 1) / 0xff;
-        c->max_speed_hz = c->baseclk;
+        c->min_speed_hz = DIV_ROUND_UP(c->baseclk, SPI_MAX_DIVIDER + 1);
+        c->max_speed_hz = c->baseclk / (SPI_MIN_DIVIDER + 1);
 
         res = platform_get_resource(dev, IORESOURCE_MEM, 0);
         if (!res)