spi: spi_mpc83xx clockrate fixes

This updates the SPI clock rate calculations for the spi_mpc83xx driver.
Some boundary conditions were wrong, and in several cases divide-by-16
wasn't always needed

Signed-off-by: Chen Gong <g.chen@freescale.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 13 deletions

diff --git a/drivers/spi/spi_mpc83xx.c b/drivers/spi/spi_mpc83xx.c
index 6832da6f7109..070c6219e2d6 100644
--- a/drivers/spi/spi_mpc83xx.c
+++ b/drivers/spi/spi_mpc83xx.c
@@ -266,21 +266,24 @@ int mpc83xx_spi_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 
         cs->hw_mode |= SPMODE_LEN(bits_per_word);
 
-        if ((mpc83xx_spi->spibrg / hz) >= 64) {
-                pm = mpc83xx_spi->spibrg / (hz * 64) - 1;
-                if (pm > 0x0f) {
-                        dev_err(&spi->dev, "Requested speed is too "
-                                "low: %d Hz. Will use %d Hz instead.\n",
-                                hz, mpc83xx_spi->spibrg / 1024);
-                        pm = 0x0f;
+        if ((mpc83xx_spi->spibrg / hz) > 64) {
+                pm = mpc83xx_spi->spibrg / (hz * 64);
+                if (pm > 16) {
+                        cs->hw_mode |= SPMODE_DIV16;
+                        pm /= 16;
+                        if (pm > 16) {
+                                dev_err(&spi->dev, "Requested speed is too "
+                                        "low: %d Hz. Will use %d Hz instead.\n",
+                                        hz, mpc83xx_spi->spibrg / 1024);
+                                pm = 16;
+                        }
                 }
-                cs->hw_mode |= SPMODE_PM(pm) | SPMODE_DIV16;
-        } else {
+        } else
                 pm = mpc83xx_spi->spibrg / (hz * 4);
-                if (pm)
-                        pm--;
-                cs->hw_mode |= SPMODE_PM(pm);
-        }
+        if (pm)
+                pm--;
+
+        cs->hw_mode |= SPMODE_PM(pm);
         regval =  mpc83xx_spi_read_reg(&mpc83xx_spi->base->mode);
         if (cs->hw_mode != regval) {
                 unsigned long flags;