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>

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index ad14f38a67e4ac91862948c1ae5ae9ab1d835de2..4e6300dc2c4e3d6fa43d4b618ca34d5e7c0b0811 100644 (file)
--- 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 357e083e8f450cec0fbe27636676f1c80a97dec5..fdb0fb9fb9aab660e2ae4b1ed0a2942d348e0dca 100644 (file)
--- 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 deea47c576e50c7ca6107f632bd215d564d376b2..f9d0c417b5a56061695e82abb781ae162c0113ae 100644 (file)
--- 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;
 }

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 758a6db864c959d3964966dabe0c54f721bbbb47..03755d4c9229d53eda40f631f71ffab4c939e2ff 100644 (file)
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -499,9 +499,13 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info,
  * @master_xfer: Issue a set of i2c transactions to the given I2C adapter
  *   defined by the msgs array, with num messages available to transfer via
  *   the adapter specified by adap.
+ * @master_xfer_atomic: same as @master_xfer. Yet, only using atomic context
+ *   so e.g. PMICs can be accessed very late before shutdown. Optional.
  * @smbus_xfer: Issue smbus transactions to the given I2C adapter. If this
  *   is not present, then the bus layer will try and convert the SMBus calls
  *   into I2C transfers instead.
+ * @smbus_xfer_atomic: same as @smbus_xfer. Yet, only using atomic context
+ *   so e.g. PMICs can be accessed very late before shutdown. Optional.
  * @functionality: Return the flags that this algorithm/adapter pair supports
  *   from the I2C_FUNC_* flags.
  * @reg_slave: Register given client to I2C slave mode of this adapter
@@ -512,9 +516,9 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info,
  * be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584
  * to name two of the most common.
  *
- * The return codes from the @master_xfer field should indicate the type of
- * error code that occurred during the transfer, as documented in the kernel
- * Documentation file Documentation/i2c/fault-codes.
+ * The return codes from the @master_xfer{_atomic} fields should indicate the
+ * type of error code that occurred during the transfer, as documented in the
+ * Kernel Documentation file Documentation/i2c/fault-codes.
  */
 struct i2c_algorithm {
        /*
@@ -528,9 +532,14 @@ struct i2c_algorithm {
         */
        int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,
                           int num);
+       int (*master_xfer_atomic)(struct i2c_adapter *adap,
+                                  struct i2c_msg *msgs, int num);
        int (*smbus_xfer)(struct i2c_adapter *adap, u16 addr,
                          unsigned short flags, char read_write,
                          u8 command, int size, union i2c_smbus_data *data);
+       int (*smbus_xfer_atomic)(struct i2c_adapter *adap, u16 addr,
+                                unsigned short flags, char read_write,
+                                u8 command, int size, union i2c_smbus_data *data);
 
        /* To determine what the adapter supports */
        u32 (*functionality)(struct i2c_adapter *adap);