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authorAlexander Sverdlin <alexander.sverdlin@nokia.com>2015-06-11 11:35:26 +0200
committerWolfram Sang <wsa@the-dreams.de>2015-06-17 14:40:58 +0200
commit955fc950795d1c9f11f220f449ecb29b92985ee2 (patch)
tree3481aae74b60bf152ca42066166c8e79ae31b38d /drivers/i2c
parent0a8237ae319ab5988d40a7a9b33d68846aae34b4 (diff)
downloadlinux-955fc950795d1c9f11f220f449ecb29b92985ee2.tar.bz2
i2c: davinci: Optimize SCL generation
There are several cases where current clock configuration algorithm produces not optimal results: - truncation in "clk" calculation leads to the fact that actual BUS frequency will be always higher than spec except two exact module frequences 8MHz and 12MHz in the whole 7-12MHz range of permitted frequences - driver configures SCL HIGH to LOW ratio always 1 to 1 and this doesn't work well in 400kHz case, namely minimum time of LOW state (according to I2C Spec 2.1) 1.3us will not be fulfilled. HIGH to LOW ratio 1 to 2 would be more approriate here. Signed-off-by: Michael Lawnick <michael.lawnick@nokia.com> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Diffstat (limited to 'drivers/i2c')
-rw-r--r--drivers/i2c/busses/i2c-davinci.c27
1 files changed, 24 insertions, 3 deletions
diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
index 3d3ae52b6916..3fbb9a035532 100644
--- a/drivers/i2c/busses/i2c-davinci.c
+++ b/drivers/i2c/busses/i2c-davinci.c
@@ -204,9 +204,30 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
psc++; /* better to run under spec than over */
d = (psc >= 2) ? 5 : 7 - psc;
- clk = ((input_clock / (psc + 1)) / (pdata->bus_freq * 1000)) - (d << 1);
- clkh = clk >> 1;
- clkl = clk - clkh;
+ clk = ((input_clock / (psc + 1)) / (pdata->bus_freq * 1000));
+ /* Avoid driving the bus too fast because of rounding errors above */
+ if (input_clock / (psc + 1) / clk > pdata->bus_freq * 1000)
+ clk++;
+ /*
+ * According to I2C-BUS Spec 2.1, in FAST-MODE LOW period should be at
+ * least 1.3uS, which is not the case with 50% duty cycle. Driving HIGH
+ * to LOW ratio as 1 to 2 is more safe.
+ */
+ if (pdata->bus_freq > 100)
+ clkl = (clk << 1) / 3;
+ else
+ clkl = (clk >> 1);
+ /*
+ * It's not always possible to have 1 to 2 ratio when d=7, so fall back
+ * to minimal possible clkh in this case.
+ */
+ if (clk >= clkl + d) {
+ clkh = clk - clkl - d;
+ clkl -= d;
+ } else {
+ clkh = 0;
+ clkl = clk - (d << 1);
+ }
davinci_i2c_write_reg(dev, DAVINCI_I2C_PSC_REG, psc);
davinci_i2c_write_reg(dev, DAVINCI_I2C_CLKH_REG, clkh);