i2c: bcm2835: Avoid clock stretching timeouts

The CLKT register contains at poweron 0x40, which at our typical 100kHz
bus rate means .64ms. But there is no specified limit to how long devices
should be able to stretch the clocks, so just disable the timeout. We
still have a timeout wrapping the entire transfer.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
BugLink: https://github.com/raspberrypi/linux/issues/3064
Signed-off-by: Wolfram Sang <wsa@kernel.org>

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index dfc5340..5149454 100644 (file)
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -23,6 +23,11 @@
 #define BCM2835_I2C_FIFO       0x10
 #define BCM2835_I2C_DIV                0x14
 #define BCM2835_I2C_DEL                0x18
+/*
+ * 16-bit field for the number of SCL cycles to wait after rising SCL
+ * before deciding the slave is not responding. 0 disables the
+ * timeout detection.
+ */
 #define BCM2835_I2C_CLKT       0x1c
 
 #define BCM2835_I2C_C_READ     BIT(0)
@@ -474,6 +479,12 @@ static int bcm2835_i2c_probe(struct platform_device *pdev)
        adap->dev.of_node = pdev->dev.of_node;
        adap->quirks = of_device_get_match_data(&pdev->dev);
 
+       /*
+        * Disable the hardware clock stretching timeout. SMBUS
+        * specifies a limit for how long the device can stretch the
+        * clock, but core I2C doesn't.
+        */
+       bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_CLKT, 0);
        bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, 0);
 
        ret = i2c_add_adapter(adap);