This adds a new I2C_M_FORCE_STOP flag that forces a stop condition after
the message in a combined transaction.
This flag is intended to be used by the devices that don't support
repeated starts like SCCB (Serial Camera Control Bus) devices.
Here is an example usage for ov772x driver that needs to issue two
separated I2C messages as the ov772x device doesn't support repeated
starts.
static int ov772x_read(struct i2c_client *client, u8 addr)
{
u8 val;
struct i2c_msg msg[] = {
{
.addr = client->addr,
.flags = I2C_M_FORCE_STOP,
.len = 1,
.buf = &addr,
},
{
.addr = client->addr,
.flags = I2C_M_RD,
.len = 1,
.buf = &val,
},
};
int ret;
ret = i2c_transfer(client->adapter, msg, 2);
if (ret != 2)
return (ret < 0) ? ret : -EIO;
return val;
}
This is another approach based on Mauro's advise for the initial attempt
(http://patchwork.ozlabs.org/patch/905192/).
Cc: Sebastian Reichel <[email protected]>
Cc: Wolfram Sang <[email protected]>
Cc: Jacopo Mondi <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Cc: Hans Verkuil <[email protected]>
Cc: Sakari Ailus <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Signed-off-by: Akinobu Mita <[email protected]>
---
drivers/i2c/i2c-core-base.c | 46 ++++++++++++++++++++++++++++++++++-----------
include/uapi/linux/i2c.h | 1 +
2 files changed, 36 insertions(+), 11 deletions(-)
diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 1ba40bb..6b73484 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1828,6 +1828,25 @@ static int i2c_check_for_quirks(struct i2c_adapter
*adap, struct i2c_msg *msgs,
return 0;
}
+static int i2c_transfer_nolock(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;
+}
+
/**
* __i2c_transfer - unlocked flavor of i2c_transfer
* @adap: Handle to I2C bus
@@ -1842,8 +1861,8 @@ static int i2c_check_for_quirks(struct i2c_adapter *adap,
struct i2c_msg *msgs,
*/
int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
- unsigned long orig_jiffies;
- int ret, try;
+ int ret;
+ int i, n;
if (WARN_ON(!msgs || num < 1))
return -EINVAL;
@@ -1857,7 +1876,6 @@ int __i2c_transfer(struct i2c_adapter *adap, struct
i2c_msg *msgs, int num)
* being executed when not needed.
*/
if (static_branch_unlikely(&i2c_trace_msg_key)) {
- int i;
for (i = 0; i < num; i++)
if (msgs[i].flags & I2C_M_RD)
trace_i2c_read(adap, &msgs[i], i);
@@ -1865,18 +1883,24 @@ int __i2c_transfer(struct i2c_adapter *adap, struct
i2c_msg *msgs, int num)
trace_i2c_write(adap, &msgs[i], i);
}
- /* 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))
+ for (i = 0; i < num; i += n) {
+ for (n = 0; i + n < num; n++) {
+ if (msgs[i + n].flags & I2C_M_FORCE_STOP) {
+ n++;
+ break;
+ }
+ }
+
+ ret = i2c_transfer_nolock(adap, &msgs[i], n);
+ if (ret != n) {
+ if (i > 0)
+ ret = (ret < 0) ? i : i + ret;
break;
+ }
+ ret = i + n;
}
if (static_branch_unlikely(&i2c_trace_msg_key)) {
- int i;
for (i = 0; i < ret; i++)
if (msgs[i].flags & I2C_M_RD)
trace_i2c_reply(adap, &msgs[i], i);
diff --git a/include/uapi/linux/i2c.h b/include/uapi/linux/i2c.h
index f71a175..36e8c7c 100644
--- a/include/uapi/linux/i2c.h
+++ b/include/uapi/linux/i2c.h
@@ -72,6 +72,7 @@ struct i2c_msg {
#define I2C_M_RD 0x0001 /* read data, from slave to master */
/* I2C_M_RD is guaranteed to be 0x0001!
*/
#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */
+#define I2C_M_FORCE_STOP 0x0100 /* force a stop condition after the
message */
#define I2C_M_DMA_SAFE 0x0200 /* the buffer of this message is DMA
safe */
/* makes only sense in kernelspace */
/* userspace buffers are copied anyway
*/
--
2.7.4
