i2c: core: Add support for best effort block read emulation

There are devices that need to handle block transactions
regardless of the capabilities exported by the adapter.
For performance reasons, they need to use i2c read blocks
if available, otherwise emulate the block transaction with word
or byte transactions.

Add support for a helper function that would read a data block
using the best transfer available: I2C_FUNC_SMBUS_READ_I2C_BLOCK,
I2C_FUNC_SMBUS_READ_WORD_DATA or I2C_FUNC_SMBUS_READ_BYTE_DATA.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index a6780289c61d207085db0b4e61590183816733de..98f6c75b1d18e4d685d381d6c1b43056b3c99452 100644 (file)
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -3007,6 +3007,63 @@ trace:
 }
 EXPORT_SYMBOL(i2c_smbus_xfer);
 
+/**
+ * i2c_smbus_read_i2c_block_data_or_emulated - read block or emulate
+ * @client: Handle to slave device
+ * @command: Byte interpreted by slave
+ * @length: Size of data block; SMBus allows at most I2C_SMBUS_BLOCK_MAX bytes
+ * @values: Byte array into which data will be read; big enough to hold
+ *     the data returned by the slave.  SMBus allows at most
+ *     I2C_SMBUS_BLOCK_MAX bytes.
+ *
+ * This executes the SMBus "block read" protocol if supported by the adapter.
+ * If block read is not supported, it emulates it using either word or byte
+ * read protocols depending on availability.
+ *
+ * The addresses of the I2C slave device that are accessed with this function
+ * must be mapped to a linear region, so that a block read will have the same
+ * effect as a byte read. Before using this function you must double-check
+ * if the I2C slave does support exchanging a block transfer with a byte
+ * transfer.
+ */
+s32 i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client,
+                                             u8 command, u8 length, u8 *values)
+{
+       u8 i = 0;
+       int status;
+
+       if (length > I2C_SMBUS_BLOCK_MAX)
+               length = I2C_SMBUS_BLOCK_MAX;
+
+       if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_I2C_BLOCK))
+               return i2c_smbus_read_i2c_block_data(client, command, length, values);
+
+       if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_BYTE_DATA))
+               return -EOPNOTSUPP;
+
+       if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_WORD_DATA)) {
+               while ((i + 2) <= length) {
+                       status = i2c_smbus_read_word_data(client, command + i);
+                       if (status < 0)
+                               return status;
+                       values[i] = status & 0xff;
+                       values[i + 1] = status >> 8;
+                       i += 2;
+               }
+       }
+
+       while (i < length) {
+               status = i2c_smbus_read_byte_data(client, command + i);
+               if (status < 0)
+                       return status;
+               values[i] = status;
+               i++;
+       }
+
+       return i;
+}
+EXPORT_SYMBOL(i2c_smbus_read_i2c_block_data_or_emulated);
+
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
 int i2c_slave_register(struct i2c_client *client, i2c_slave_cb_t slave_cb)
 {

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 5aea071372185e47f002a88edafed00b3d7acbac..768063baafbf5efe6c122a123b0c3f9bfe3bd050 100644 (file)
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -121,6 +121,9 @@ extern s32 i2c_smbus_read_i2c_block_data(const struct i2c_client *client,
 extern s32 i2c_smbus_write_i2c_block_data(const struct i2c_client *client,
                                          u8 command, u8 length,
                                          const u8 *values);
+extern s32
+i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client,
+                                         u8 command, u8 length, u8 *values);
 #endif /* I2C */
 
 /**