On Wed, 16 Sep 2009 14:17:09 +0300, Mika Kuoppala wrote:
> Low priority thread holding the i2c bus mutex could block
> more high 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@xxxxxxxxx>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> ---
> drivers/i2c/i2c-core.c | 12 ++++++------
> include/linux/i2c.h | 3 +--
> 2 files changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 0e45c29..40f645f 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -548,7 +548,7 @@ 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)
> @@ -1018,12 +1018,12 @@ 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);
Hmm, rt_mutex doesn't handle locking model validation as regular
mutexes have? Looks like a regression to me.
> }
>
> /* Retry automatically on arbitration loss */
> @@ -1035,7 +1035,7 @@ 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 {
> @@ -1839,7 +1839,7 @@ 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;
> @@ -1853,7 +1853,7 @@ 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);
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index f4784c0..ddca85d 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -340,8 +340,7 @@ 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;
--
Jean Delvare
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