[PATCH] i2c: rk3x: fix divisor calculation for SCL frequency

[Addy Ke]

I2C_CLKDIV register descripted in the previous version of
RK3x chip manual is incorrect. Plus 1 is required.

The correct formula:
- T(SCL_HIGH) = T(PCLK) * (CLKDIVH + 1) * 8
- T(SCL_LOW) = T(PCLK) * (CLKDIVL + 1) * 8
- (SCL Divsor) = 8 * ((CLKDIVL + 1) + (CLKDIVH + 1))
- SCL = PCLK / (CLK Divsor)

It will be updated to the latest version of chip manual.

Signed-off-by: Addy Ke <addy.ke at rock-chips.com>
---
 drivers/i2c/busses/i2c-rk3x.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
index e637c32..76b6604 100644
--- a/drivers/i2c/busses/i2c-rk3x.c
+++ b/drivers/i2c/busses/i2c-rk3x.c
@@ -433,8 +433,8 @@ static void rk3x_i2c_set_scl_rate(struct rk3x_i2c *i2c, unsigned long scl_rate)
 	unsigned long i2c_rate = clk_get_rate(i2c->clk);
 	unsigned int div;
 
-	/* SCL rate = (clk rate) / (8 * DIV) */
-	div = DIV_ROUND_UP(i2c_rate, scl_rate * 8);
+	/* SCL rate = (clk rate) / (8 * (DIV + 2)) */
+	div = DIV_ROUND_UP(i2c_rate, scl_rate * 8) - 2;
 
 	/* The lower and upper half of the CLKDIV reg describe the length of
 	 * SCL low & high periods. */
-- 
1.8.3.2