i2c: core: introduce callbacks for atomic transfers

We had the request to access devices very late when interrupts are not
available anymore multiple times now. Mostly to prepare shutdown or
reboot. Allow adapters to specify a specific callback for this case.
Note that we fall back to the generic {master|smbus}_xfer callback if
this new atomic one is not present. This is intentional to preserve the
previous behaviour and avoid regressions. Because there are drivers not
using interrupts or because it might have worked "accidently" before.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Stefan Lengfeld <contact@stefanchrist.eu>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

3 files changed, 24 insertions, 7 deletions

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index ad14f38a67e4..4e6300dc2c4e 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1890,7 +1890,11 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	/* 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 (i2c_in_atomic_xfer_mode() && adap->algo->master_xfer_atomic)
+			ret = adap->algo->master_xfer_atomic(adap, msgs, num);
+		else
+			ret = adap->algo->master_xfer(adap, msgs, num);
+
 		if (ret != -EAGAIN)
 			break;
 		if (time_after(jiffies, orig_jiffies + adap->timeout))
diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 357e083e8f45..fdb0fb9fb9aa 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -548,6 +548,9 @@ s32 __i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
 		     unsigned short flags, char read_write,
 		     u8 command, int protocol, union i2c_smbus_data *data)
 {
+	int (*xfer_func)(struct i2c_adapter *adap, u16 addr,
+			 unsigned short flags, char read_write,
+			 u8 command, int size, union i2c_smbus_data *data);
 	unsigned long orig_jiffies;
 	int try;
 	s32 res;
@@ -562,13 +565,20 @@ s32 __i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
 
 	flags &= I2C_M_TEN | I2C_CLIENT_PEC | I2C_CLIENT_SCCB;
 
-	if (adapter->algo->smbus_xfer) {
+	xfer_func = adapter->algo->smbus_xfer;
+	if (i2c_in_atomic_xfer_mode()) {
+		if (adapter->algo->smbus_xfer_atomic)
+			xfer_func = adapter->algo->smbus_xfer_atomic;
+		else if (adapter->algo->master_xfer_atomic)
+			xfer_func = NULL; /* fallback to I2C emulation */
+	}
+
+	if (xfer_func) {
 		/* Retry automatically on arbitration loss */
 		orig_jiffies = jiffies;
 		for (res = 0, try = 0; try <= adapter->retries; try++) {
-			res = adapter->algo->smbus_xfer(adapter, addr, flags,
-							read_write, command,
-							protocol, data);
+			res = xfer_func(adapter, addr, flags, read_write,
+					command, protocol, data);
 			if (res != -EAGAIN)
 				break;
 			if (time_after(jiffies,
diff --git a/drivers/i2c/i2c-core.h b/drivers/i2c/i2c-core.h
index deea47c576e5..f9d0c417b5a5 100644
--- a/drivers/i2c/i2c-core.h
+++ b/drivers/i2c/i2c-core.h
@@ -43,10 +43,13 @@ static inline int __i2c_lock_bus_helper(struct i2c_adapter *adap)
 {
 	int ret = 0;
 
-	if (i2c_in_atomic_xfer_mode())
+	if (i2c_in_atomic_xfer_mode()) {
+		WARN(!adap->algo->master_xfer_atomic && !adap->algo->smbus_xfer_atomic,
+		     "No atomic I2C transfer handler for '%s'\n", dev_name(&adap->dev));
 		ret = i2c_trylock_bus(adap, I2C_LOCK_SEGMENT) ? 0 : -EAGAIN;
-	else
+	} else {
 		i2c_lock_bus(adap, I2C_LOCK_SEGMENT);
+	}
 
 	return ret;
 }