fixes: round down divider instead of incrementing
adds: make sure bits 16-31 of cdiv register are always 0
adds: assume minimal divider of 2 if divider resulted in 0
(bcm2835 sets divider to 32768 if cdiv is set to 0)
Signed-off-by: s. wicki <[email protected]>
---
drivers/i2c/busses/i2c-bcm2835.c | 38 +++++++++++++++++++++++++++++++-------
1 file changed, 31 insertions(+), 7 deletions(-)
diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index c9336a3..745181c 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -51,6 +51,9 @@
#define BCM2835_I2C_S_LEN BIT(10) /* Fake bit for SW error reporting */
#define BCM2835_I2C_TIMEOUT (msecs_to_jiffies(1000))
+#define BCM2835_I2C_CDIV_MIN 0x0002
+#define BCM2835_I2C_CDIV_MAX 0xFFFE
+#define BCM2835_I2C_CDIV_BITMSK 0xFFFE
struct bcm2835_i2c_dev {
struct device *dev;
@@ -251,13 +254,34 @@ static int bcm2835_i2c_probe(struct platform_device *pdev)
}
divider = DIV_ROUND_UP(clk_get_rate(i2c_dev->clk), bus_clk_rate);
- /*
- * Per the datasheet, the register is always interpreted as an even
- * number, by rounding down. In other words, the LSB is ignored. So,
- * if the LSB is set, increment the divider to avoid any issue.
- */
- if (divider & 1)
- divider++;
+ if (divider == 0) {
+ /*
+ * divider results in 0 by extremely high bus_clk_rate values
+ * such as bus_clk_rate >= 4044967297 and core_clock = 250MHz.
+ * In such a case assume the minimal possible divider since
+ * bcm2835 chip sets divisor internally to 32768 if cdiv is 0.
+ */
+ divider = BCM2835_I2C_CDIV_MIN;
+ } else {
+ /* check if divider meets certain bcm2835 specific criterias */
+ if ((divider & BCM2835_I2C_CDIV_BITMSK) != divider) {
+ if (divider > BCM2835_I2C_CDIV_MAX)
+ /*
+ * Per the datasheet it must be made sure
+ * that bits 16-31 are set to 0. If that is
+ * not the case, then set to the maximum
+ * allowed value.
+ */
+ divider = BCM2835_I2C_CDIV_MAX;
+ else
+ /*
+ * Per datasheet the cdiv is always rounded
+ * down to an even number. Bitmask takes care
+ * of this and clears the LSB
+ */
+ divider &= BCM2835_I2C_CDIV_BITMSK;
+ }
+ }
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DIV, divider);
irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
--
2.1.4
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