• Aaro Koskinen's avatar
    i2c: OMAP2/3: Fix scll/sclh calculations · baf46b4e
    Aaro Koskinen authored
    Fix scll/sclh calculations for HS and fast modes. Currently the driver
    uses equal (roughly) low/high times which will result in too short
    low time.
    
    OMAP3430 TRM gives the following equations:
    
    	F/S: tLow  = (scll + 7) * internal_clk
    	     tHigh = (sclh + 5) * internal_clk
    	HS:  tLow  = (scll + 7) * fclk
    	     tHigh = (sclh + 5) * fclk
    
    Furthermore, the I2C specification sets the following minimum values
    for HS tLow/tHigh for capacitive bus loads 100 pF (maximum speed 3400)
    and 400 pF (maximum speed 1700):
    
    	speed	tLow		tHigh
    	3400	160 ns		60 ns
    	1700	320 ns		120 ns
    
    and for F/S:
    
    	speed	tLow		tHigh
    	400	1300 ns		600 ns
    	100	4700 ns		4000 ns
    
    By using duty cycles 33/66 (HS, F) and 50/50 (S) we stay above these
    minimum values.
    Signed-off-by: default avatarAaro Koskinen <aaro.koskinen@nokia.com>
    Acked-by: default avatarTony Lindgren <tony@atomide.com>
    Signed-off-by: default avatarBen Dooks <ben-linux@fluff.org>
    baf46b4e
i2c-omap.c 25.2 KB