Some drivers (in particular for TV cards) need exclusive access to
their I2C buses for specific operations. Export an unlocked flavor
of i2c_transfer to give them full control.
The unlocked flavor has the following limitations:
* Obviously, caller must hold the i2c adapter lock.
* No debug messages are logged. We don't want to log messages while
holding a rt_mutex.
* No check is done on the existence of adap->algo->master_xfer. It
is thus the caller's responsibility to ensure that the function is
OK to call.
Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
---
Mauro, would this be OK with you?
drivers/i2c/i2c-core.c | 44 +++++++++++++++++++++++++++++++++-----------
include/linux/i2c.h | 3 +++
2 files changed, 36 insertions(+), 11 deletions(-)
--- linux-3.5-rc4.orig/drivers/i2c/i2c-core.c 2012-06-05 16:22:59.000000000 +0200
+++ linux-3.5-rc4/drivers/i2c/i2c-core.c 2012-06-29 12:41:04.707793937 +0200
@@ -1312,6 +1312,37 @@ module_exit(i2c_exit);
*/
/**
+ * __i2c_transfer - unlocked flavor of i2c_transfer
+ * @adap: Handle to I2C bus
+ * @msgs: One or more messages to execute before STOP is issued to
+ * terminate the operation; each message begins with a START.
+ * @num: Number of messages to be executed.
+ *
+ * Returns negative errno, else the number of messages executed.
+ *
+ * Adapter lock must be held when calling this function. No debug logging
+ * takes place. adap->algo->master_xfer existence isn't checked.
+ */
+int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
+{
+ unsigned long orig_jiffies;
+ int ret, try;
+
+ /* Retry automatically on arbitration loss */
+ orig_jiffies = jiffies;
+ for (ret = 0, try = 0; try <= adap->retries; try++) {
+ ret = adap->algo->master_xfer(adap, msgs, num);
+ if (ret != -EAGAIN)
+ break;
+ if (time_after(jiffies, orig_jiffies + adap->timeout))
+ break;
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL(__i2c_transfer);
+
+/**
* i2c_transfer - execute a single or combined I2C message
* @adap: Handle to I2C bus
* @msgs: One or more messages to execute before STOP is issued to
@@ -1325,8 +1356,7 @@ module_exit(i2c_exit);
*/
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
- unsigned long orig_jiffies;
- int ret, try;
+ int ret;
/* REVISIT the fault reporting model here is weak:
*
@@ -1364,15 +1394,7 @@ int i2c_transfer(struct i2c_adapter *ada
i2c_lock_adapter(adap);
}
- /* Retry automatically on arbitration loss */
- orig_jiffies = jiffies;
- for (ret = 0, try = 0; try <= adap->retries; try++) {
- ret = adap->algo->master_xfer(adap, msgs, num);
- if (ret != -EAGAIN)
- break;
- if (time_after(jiffies, orig_jiffies + adap->timeout))
- break;
- }
+ ret = __i2c_transfer(adap, msgs, num);
i2c_unlock_adapter(adap);
return ret;
--- linux-3.5-rc4.orig/include/linux/i2c.h 2012-06-05 16:23:05.000000000 +0200
+++ linux-3.5-rc4/include/linux/i2c.h 2012-06-29 10:29:47.865621249 +0200
@@ -68,6 +68,9 @@ extern int i2c_master_recv(const struct
*/
extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
int num);
+/* Unlocked flavor */
+extern int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
+ int num);
/* This is the very generalized SMBus access routine. You probably do not
want to use this, though; one of the functions below may be much easier,
--
Jean Delvare
--
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