From mboxrd@z Thu Jan 1 00:00:00 1970 From: Addy Ke Subject: [PATCH] i2c: rk3x: fix divisor calculation for SCL frequency Date: Fri, 5 Sep 2014 10:32:13 +0800 Message-ID: <1409884333-3544-1-git-send-email-addy.ke@rock-chips.com> Return-path: Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org, max.schwarz-BGeptl67XyCzQB+pC5nmwQ@public.gmane.org, heiko-4mtYJXux2i+zQB+pC5nmwQ@public.gmane.org, olof-nZhT3qVonbNeoWH0uzbU5w@public.gmane.org, dianders-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-rockchip-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, cf-TNX95d0MmH7DzftRWevZcw@public.gmane.org, xjq-TNX95d0MmH7DzftRWevZcw@public.gmane.org, huangtao-TNX95d0MmH7DzftRWevZcw@public.gmane.org, zyw-TNX95d0MmH7DzftRWevZcw@public.gmane.org, yzq-TNX95d0MmH7DzftRWevZcw@public.gmane.org, hj-TNX95d0MmH7DzftRWevZcw@public.gmane.org, kever.yang-TNX95d0MmH7DzftRWevZcw@public.gmane.org, hl-TNX95d0MmH7DzftRWevZcw@public.gmane.org, caesar.wang-TNX95d0MmH7DzftRWevZcw@public.gmane.org, zhengsq-TNX95d0MmH7DzftRWevZcw@public.gmane.org, Addy Ke List-Id: linux-i2c@vger.kernel.org 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 --- 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