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i2c: OMAP2/3: Fix scll/sclh calculations

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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: Aaro Koskinen <aaro.koskinen@nokia.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
This commit is contained in:
Aaro Koskinen 2009-05-27 17:54:45 +03:00 committed by Ben Dooks
parent e0cd2dd5dd
commit baf46b4e37
1 changed files with 18 additions and 7 deletions
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25
drivers/i2c/busses/i2c-omap.c
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@ -343,17 +343,28 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
/* If configured for High Speed */ /* If configured for High Speed */
if (dev->speed > 400) { if (dev->speed > 400) {
unsigned long scl;
/* For first phase of HS mode */ /* For first phase of HS mode */
fsscll = internal_clk / (400 * 2) - 6; scl = internal_clk / 400;
fssclh = internal_clk / (400 * 2) - 6; fsscll = scl - (scl / 3) - 7;
fssclh = (scl / 3) - 5;
/* For second phase of HS mode */ /* For second phase of HS mode */
hsscll = fclk_rate / (dev->speed * 2) - 6; scl = fclk_rate / dev->speed;
hssclh = fclk_rate / (dev->speed * 2) - 6; hsscll = scl - (scl / 3) - 7;
hssclh = (scl / 3) - 5;
} else if (dev->speed > 100) {
unsigned long scl;
/* Fast mode */
scl = internal_clk / dev->speed;
fsscll = scl - (scl / 3) - 7;
fssclh = (scl / 3) - 5;
} else { } else {
/* To handle F/S modes */ /* Standard mode */
fsscll = internal_clk / (dev->speed * 2) - 6; fsscll = internal_clk / (dev->speed * 2) - 7;
fssclh = internal_clk / (dev->speed * 2) - 6; fssclh = internal_clk / (dev->speed * 2) - 5;
} }
scll = (hsscll << OMAP_I2C_SCLL_HSSCLL) | fsscll; scll = (hsscll << OMAP_I2C_SCLL_HSSCLL) | fsscll;
sclh = (hssclh << OMAP_I2C_SCLH_HSSCLH) | fssclh; sclh = (hssclh << OMAP_I2C_SCLH_HSSCLH) | fssclh;