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 <[e-mail]>
Acked-by: Tony Lindgren <[e-mail]>
Signed-off-by: Ben Dooks <[e-mail]>

drivers/i2c/busses/i2c-omap.c

···
 
 	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 */