These changes are the raw update to linux-4.4.6-rt14. Kernel sources

[kvmfornfv.git] / kernel / drivers / i2c / busses / i2c-sirf.c

diff --git a/kernel/drivers/i2c/busses/i2c-sirf.c b/kernel/drivers/i2c/busses/i2c-sirf.c
index 1092d4e..13e51ef 100644 (file)
--- a/kernel/drivers/i2c/busses/i2c-sirf.c
+++ b/kernel/drivers/i2c/busses/i2c-sirf.c
@@ -358,11 +358,29 @@ static int i2c_sirfsoc_probe(struct platform_device *pdev)
        if (err < 0)
                bitrate = SIRFSOC_I2C_DEFAULT_SPEED;
 
-       if (bitrate < 100000)
-               regval =
-                       (2 * ctrl_speed) / (bitrate * 11);
-       else
+       /*
+        * Due to some hardware design issues, we need to tune the formula.
+        * Since i2c is open drain interface that allows the slave to
+        * stall the transaction by holding the SCL line at '0', the RTL
+        * implementation is waiting for SCL feedback from the pin after
+        * setting it to High-Z ('1'). This wait adds to the high-time
+        * interval counter few cycles of the input synchronization
+        * (depending on the SCL_FILTER_REG field), and also the time it
+        * takes for the board pull-up resistor to rise the SCL line.
+        * For slow SCL settings these additions are negligible,
+        * but they start to affect the speed when clock is set to faster
+        * frequencies.
+        * Through the actual tests, use the different user_div value(which
+        * in the divider formular 'Fio / (Fi2c * user_div)') to adapt
+        * the different ranges of i2c bus clock frequency, to make the SCL
+        * more accurate.
+        */
+       if (bitrate <= 30000)
                regval = ctrl_speed / (bitrate * 5);
+       else if (bitrate > 30000 && bitrate <= 280000)
+               regval = (2 * ctrl_speed) / (bitrate * 11);
+       else
+               regval = ctrl_speed / (bitrate * 6);
 
        writel(regval, siic->base + SIRFSOC_I2C_CLK_CTRL);
        if (regval > 0xFF)