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@xxxxxxxxx>
---
drivers/i2c/busses/i2c-omap.c | 25 ++++++++++++++++++-------
1 files changed, 18 insertions(+), 7 deletions(-)
diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index 9919c08..5d9880c 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -343,17 +343,28 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
/* If configured for High Speed */
if (dev->speed > 400) {
+ unsigned long scl;
+
/* For first phase of HS mode */
- fsscll = internal_clk / (400 * 2) - 6;
- fssclh = internal_clk / (400 * 2) - 6;
+ scl = internal_clk / 400;
+ fsscll = scl - (scl / 3) - 7;
+ fssclh = (scl / 3) - 5;
/* For second phase of HS mode */
- hsscll = fclk_rate / (dev->speed * 2) - 6;
- hssclh = fclk_rate / (dev->speed * 2) - 6;
+ scl = fclk_rate / dev->speed;
+ 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 {
- /* To handle F/S modes */
- fsscll = internal_clk / (dev->speed * 2) - 6;
- fssclh = internal_clk / (dev->speed * 2) - 6;
+ /* Standard mode */
+ fsscll = internal_clk / (dev->speed * 2) - 7;
+ fssclh = internal_clk / (dev->speed * 2) - 5;
}
scll = (hsscll << OMAP_I2C_SCLL_HSSCLL) | fsscll;
sclh = (hssclh << OMAP_I2C_SCLH_HSSCLH) | fssclh;
--
1.5.4.3
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