i2c: OMAP3: Better noise suppression for fast/standard modes

Use longer noise filter period for fast and standard mode. Based on an
earlier patch by Eero Nurkkala.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index a879e4bf5122..c73475dd0fba 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -333,8 +333,18 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
 
         if (cpu_is_omap2430() || cpu_is_omap34xx()) {
 
-                /* HSI2C controller internal clk rate should be 19.2 Mhz */
-                internal_clk = 19200;
+                /*
+                 * HSI2C controller internal clk rate should be 19.2 Mhz for
+                 * HS and for all modes on 2430. On 34xx we can use lower rate
+                 * to get longer filter period for better noise suppression.
+                 * The filter is iclk (fclk for HS) period.
+                 */
+                if (dev->speed > 400 || cpu_is_omap_2430())
+                        internal_clk = 19200;
+                else if (dev->speed > 100)
+                        internal_clk = 9600;
+                else
+                        internal_clk = 4000;
                 fclk_rate = clk_get_rate(dev->fclk) / 1000;
 
                 /* Compute prescaler divisor */