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i2c: rk3x: fix divisor calculation for SCL frequency 

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@rock-chips.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org
This commit is contained in:
addy ke 2014-09-08 11:38:25 +08:00 committed by Wolfram Sang
parent a4780d039c
commit b4a7bd7a38
1 changed files with 5 additions and 6 deletions
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11
drivers/i2c/busses/i2c-rk3x.c
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@ -433,12 +433,11 @@ 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);
/* The lower and upper half of the CLKDIV reg describe the length of
* SCL low & high periods. */
div = DIV_ROUND_UP(div, 2);
/* set DIV = DIVH = DIVL
* SCL rate = (clk rate) / (8 * (DIVH + 1 + DIVL + 1))
* = (clk rate) / (16 * (DIV + 1))
*/
div = DIV_ROUND_UP(i2c_rate, scl_rate * 16) - 1;
i2c_writel(i2c, (div << 16) | (div & 0xffff), REG_CLKDIV);
}