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i2c: Prevent priority inversion on top of bus lock

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Low priority thread holding the i2c bus mutex could block higher
priority threads to access the bus resulting in unacceptable
latencies. Change the mutex type to rt_mutex preventing priority
inversion.

Tested-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@nokia.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
This commit is contained in:
Mika Kuoppala 2009-12-06 17:06:22 +01:00 committed by Jean Delvare
parent a0c11cdd6a
commit 194684e596
3 changed files with 10 additions and 10 deletions
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1
drivers/i2c/Kconfig
View file

@ -5,6 +5,7 @@
menuconfig I2C
tristate "I2C support"
depends on HAS_IOMEM
select RT_MUTEXES
---help---
I2C (pronounce: I-square-C) is a slow serial bus protocol used in
many micro controller applications and developed by Philips. SMBus,

12
drivers/i2c/i2c-core.c
View file

@ -584,7 +584,7 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
goto out_list;
}
mutex_init(&adap->bus_lock);
rt_mutex_init(&adap->bus_lock);
/* Set default timeout to 1 second if not already set */
if (adap->timeout == 0)
@ -1092,12 +1092,12 @@ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
#endif
if (in_atomic() || irqs_disabled()) {
ret = mutex_trylock(&adap->bus_lock);
ret = rt_mutex_trylock(&adap->bus_lock);
if (!ret)
/* I2C activity is ongoing. */
return -EAGAIN;
} else {
mutex_lock_nested(&adap->bus_lock, adap->level);
rt_mutex_lock(&adap->bus_lock);
}
/* Retry automatically on arbitration loss */
@ -1109,7 +1109,7 @@ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
if (time_after(jiffies, orig_jiffies + adap->timeout))
break;
}
mutex_unlock(&adap->bus_lock);
rt_mutex_unlock(&adap->bus_lock);
return ret;
} else {
@ -1913,7 +1913,7 @@ s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
flags &= I2C_M_TEN | I2C_CLIENT_PEC;
if (adapter->algo->smbus_xfer) {
mutex_lock(&adapter->bus_lock);
rt_mutex_lock(&adapter->bus_lock);
/* Retry automatically on arbitration loss */
orig_jiffies = jiffies;
@ -1927,7 +1927,7 @@ s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
orig_jiffies + adapter->timeout))
break;
}
mutex_unlock(&adapter->bus_lock);
rt_mutex_unlock(&adapter->bus_lock);
} else
res = i2c_smbus_xfer_emulated(adapter,addr,flags,read_write,
command, protocol, data);

7
include/linux/i2c.h
View file

@ -338,8 +338,7 @@ struct i2c_adapter {
void *algo_data;
/* data fields that are valid for all devices */
u8 level; /* nesting level for lockdep */
struct mutex bus_lock;
struct rt_mutex bus_lock;
int timeout; /* in jiffies */
int retries;
@ -367,7 +366,7 @@ static inline void i2c_set_adapdata(struct i2c_adapter *dev, void *data)
*/
static inline void i2c_lock_adapter(struct i2c_adapter *adapter)
{
mutex_lock(&adapter->bus_lock);
rt_mutex_lock(&adapter->bus_lock);
}
/**
@ -376,7 +375,7 @@ static inline void i2c_lock_adapter(struct i2c_adapter *adapter)
*/
static inline void i2c_unlock_adapter(struct i2c_adapter *adapter)
{
mutex_unlock(&adapter->bus_lock);
rt_mutex_unlock(&adapter->bus_lock);
}
/*flags for the client struct: */