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i2c: bcm2835: clear reserved bits in S-Register

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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>
This commit is contained in:
Silvan Wicki 2015-06-16 17:40:59 +02:00 committed by Wolfram Sang
parent b6eba5598d
commit 7b618638a5
1 changed files with 3 additions and 0 deletions
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3
drivers/i2c/busses/i2c-bcm2835.c
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@ -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);