[PATCH] i2c: core: add support for read commands longer than byte

[Crt Mori <cmo-fc6wVz46lShBDgjK7y7TUQ@public.gmane.org>]

If you want to send more than 1 byte as command to slave you need to go away
from the smbus (which has a 8 bit command defined in specification). i2c has
no such limitation in specification and since we want to have a longer than
1 byte command, we need additional function to handle it. With outside
buffers we have also avoided endianness problems (if we would just define a
u16 command instead of u8). Also there are now no limitations (as per i2c
specification) of command length.
Addressed read function is when we have a slave device which accepts commands
longer than byte or some subcommands in same write string before issuing a
repeat start before read cycle to read more than byte (or byte) from slave
device.

Signed-off-by: Crt Mori <cmo-fc6wVz46lShBDgjK7y7TUQ@public.gmane.org>
---
 drivers/i2c/i2c-core.c | 40 ++++++++++++++++++++++++++++++++++++++++
 include/linux/i2c.h    |  4 ++++
 2 files changed, 44 insertions(+)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 069a41f..bccf83f 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -2980,6 +2980,46 @@ int i2c_slave_unregister(struct i2c_client *client)
 EXPORT_SYMBOL_GPL(i2c_slave_unregister);
 #endif
 
+/**
+ * i2c_addressed_read - writes read commands with desired length and read
+ * desired length of data.
+ * @client: Handle to slave device
+ * @command: Pointer to command location
+ * @cmd_len: Number of command bytes on command location
+ * @data: Pointer to read data location
+ * @data_len: Expected number of read bytes
+ *
+ * Addressed read on slave device when command is longer than byte. Returns
+ * negative errno on error and 0 on success.
+ */
+s32 i2c_addressed_read(const struct i2c_client *client, u8 *command,
+		       u16 cmd_len, u8 *data, u16 data_len)
+{
+	s32 status;
+	struct i2c_msg msg[2] =	{
+		{
+			.addr = client->addr,
+			.flags = client->flags,
+			.len = cmd_len,
+			.buf = command,
+		},
+		{
+			.addr = client->addr,
+			.flags = client->flags | I2C_M_RD,
+			.len = data_len,
+			.buf = data,
+		},
+	};
+
+	status = i2c_transfer(client->adapter, msg, 2);
+
+	if (status < 0)
+		return status;
+
+	return 0;
+}
+EXPORT_SYMBOL(i2c_addressed_read);
+
 MODULE_AUTHOR("Simon G. Vogl <simon-nD9nYVNVf00W+b/DJNNodF6hYfS7NtTn@public.gmane.org>");
 MODULE_DESCRIPTION("I2C-Bus main module");
 MODULE_LICENSE("GPL");
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index e83a738..d3cc1af 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -121,6 +121,10 @@ 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);
+
+s32 i2c_addressed_read(const struct i2c_client *client, u8 *command,
+		       u16 cmd_len, u8 *data, u16 data_len);
+
 #endif /* I2C */
 
 /**
-- 
2.1.4