Commit 194684e5 authored by Mika Kuoppala's avatar Mika Kuoppala Committed by Jean Delvare
Browse files

i2c: Prevent priority inversion on top of bus lock 



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: default avatarPeter Ujfalusi <peter.ujfalusi@nokia.com>
Signed-off-by: default avatarMika Kuoppala <mika.kuoppala@nokia.com>
Signed-off-by: default avatarJean Delvare <khali@linux-fr.org>
parent a0c11cdd

drivers/i2c/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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,

drivers/i2c/i2c-core.c

+6 −6
Original line number Diff line number Diff line
@@ -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);

include/linux/i2c.h

+3 −4
Original line number Diff line number Diff line
@@ -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: */