Patch "i2c: ismt: Separate I2C block read from SMBus block read" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

i2c: ismt: Separate I2C block read from SMBus block read

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
i2c-ismt-separate-i2c-block-read-from-smbus-block-read.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Pontus Andersson <[email protected]>
Date: Mon, 2 Oct 2017 14:45:19 +0200
Subject: i2c: ismt: Separate I2C block read from SMBus block read

From: Pontus Andersson <[email protected]>

commit c6ebcedbab7ca78984959386012a17b21183e1a3 upstream.

Commit b6c159a9cb69 ("i2c: ismt: Don't duplicate the receive length for block reads") broke I2C block reads. It aimed to fix normal SMBus block read, but changed the correct behavior of I2C block read in the process.

According to Documentation/i2c/smbus-protocol, one vital difference between normal SMBus block read and I2C block read is that there is no byte count prefixed in the data sent on the wire:

SMBus Block Read: i2c_smbus_read_block_data()
S Addr Wr [A] Comm [A]
S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P

I2C Block Read: i2c_smbus_read_i2c_block_data()
S Addr Wr [A] Comm [A]
S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P

Therefore the two transaction types need to be processed differently in the driver by copying of the dma_buffer as done previously for the I2C_SMBUS_I2C_BLOCK_DATA case.

---
 drivers/i2c/busses/i2c-ismt.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

@@ -340,12 +340,15 @@ static int ismt_process_desc(const struc
 			data->word = dma_buffer[0] | (dma_buffer[1] << 8);
 			break;
 		case I2C_SMBUS_BLOCK_DATA:
-		case I2C_SMBUS_I2C_BLOCK_DATA:
 			if (desc->rxbytes != dma_buffer[0] + 1)
 				return -EMSGSIZE;
 
 			memcpy(data->block, dma_buffer, desc->rxbytes);
 			break;
+		case I2C_SMBUS_I2C_BLOCK_DATA:
+			memcpy(&data->block[1], dma_buffer, desc->rxbytes);
+			data->block[0] = desc->rxbytes;
+			break;
 		}
 		return 0;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/i2c-ismt-separate-i2c-block-read-from-smbus-block-read.patch