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Subject[PATCH] i2c-algo-bit: Fix spurious SCL timeouts under heavy load
Date
When the system is under heavy load, there can be a significant delay
between the getscl() and time_after() calls inside sclhi(). That delay
may cause the time_after() check to trigger after SCL has gone high,
causing sclhi() to return -ETIMEDOUT.

To fix the problem, double check that SCL is still low after the
timeout has been reached, before deciding to return -ETIMEDOUT.

Signed-off-by: Ville Syrjälä <syrjala@sci.fi>
---
I can easily reproduce these spurious timeouts on my HP-compaq nc6000
laptop with the radeon kms driver. It's enough to have a -j2 kernel
build running, and simultaneosly issue xrandr commands in a
terminal. Calling xrandr will cause the driver to re-read the EDID
from the display. A significant number of the EDID reads will fail.
With this fix I have yet to see any failed EDID reads.
drivers/i2c/algos/i2c-algo-bit.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)
diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c
index 525c734..d25112e 100644
--- a/drivers/i2c/algos/i2c-algo-bit.c
+++ b/drivers/i2c/algos/i2c-algo-bit.c
@@ -104,9 +104,11 @@ static int sclhi(struct i2c_algo_bit_data *adap)
* are processing data internally.
*/
if (time_after(jiffies, start + adap->timeout))
- return -ETIMEDOUT;
+ break;
cond_resched();
}
+ if (!getscl(adap))
+ return -ETIMEDOUT;
#ifdef DEBUG
if (jiffies != start && i2c_debug >= 3)
pr_debug("i2c-algo-bit: needed %ld jiffies for SCL to go "
--
1.7.3.4
--
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