i2c: bcm2835: clear reserved bits in S-Register

The datasheet mentions on page 31 that the bits 10-31 must be read as
don't care and written as 0.
https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf

We cannot guarantee that we read bits 10-31 as always 0 (because the
datasheet says read as don't care). We clear the bits with a bitmask to
prevent writing back unknown data at the reserved bits.

Signed-off-by: Silvan Wicki <linux_wi@tinag.ch>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index c9336a3202d5620681b38d6e8c2b47651a75af0e..aa06da17e30e7b6b0e95c60fbc31ca76365f2510 100644 (file)
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -50,6 +50,8 @@
 #define BCM2835_I2C_S_CLKT     BIT(9)
 #define BCM2835_I2C_S_LEN      BIT(10) /* Fake bit for SW error reporting */
 
+#define BCM2835_I2C_BITMSK_S   0x03FF
+
 #define BCM2835_I2C_TIMEOUT (msecs_to_jiffies(1000))
 
 struct bcm2835_i2c_dev {
@@ -111,6 +113,7 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
        u32 val, err;
 
        val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+       val &= BCM2835_I2C_BITMSK_S;
        bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, val);
 
        err = val & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);