Linux-libre 4.4-gnupck-4.4-gnu

1 files changed, 17 insertions, 2 deletions

diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
index 3fbb9a035..a8bdcb529 100644
--- a/drivers/i2c/busses/i2c-davinci.c
+++ b/drivers/i2c/busses/i2c-davinci.c
@@ -181,6 +181,7 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
 	u32 clkh;
 	u32 clkl;
 	u32 input_clock = clk_get_rate(dev->clk);
+	struct device_node *of_node = dev->dev->of_node;
 
 	/* NOTE: I2C Clock divider programming info
 	 * As per I2C specs the following formulas provide prescaler
@@ -196,14 +197,27 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
 	 * where if PSC == 0, d = 7,
 	 *       if PSC == 1, d = 6
 	 *       if PSC > 1 , d = 5
+	 *
+	 * Note:
+	 * d is always 6 on Keystone I2C controller
 	 */
 
-	/* get minimum of 7 MHz clock, but max of 12 MHz */
-	psc = (input_clock / 7000000) - 1;
+	/*
+	 * Both Davinci and current Keystone User Guides recommend a value
+	 * between 7MHz and 12MHz. In reality 7MHz module clock doesn't
+	 * always produce enough margin between SDA and SCL transitions.
+	 * Measurements show that the higher the module clock is, the
+	 * bigger is the margin, providing more reliable communication.
+	 * So we better target for 12MHz.
+	 */
+	psc = (input_clock / 12000000) - 1;
 	if ((input_clock / (psc + 1)) > 12000000)
 		psc++;	/* better to run under spec than over */
 	d = (psc >= 2) ? 5 : 7 - psc;
 
+	if (of_node && of_device_is_compatible(of_node, "ti,keystone-i2c"))
+		d = 6;
+
 	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)
@@ -726,6 +740,7 @@ static struct i2c_algorithm i2c_davinci_algo = {
 
 static const struct of_device_id davinci_i2c_of_match[] = {
 	{.compatible = "ti,davinci-i2c", },
+	{.compatible = "ti,keystone-i2c", },
 	{},
 };
 MODULE_DEVICE_TABLE(of, davinci_i2c_of_match);