linux-kernel - [PATCH 4.4 16/27] i2c: ismt: Separate I2C block read from SMBus block read

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Date:   Tue, 24 Oct 2017 14:58:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pontus Andersson <epontan@...il.com>,
        Stephen Douthit <stephend@...engineering.com>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: [PATCH 4.4 16/27] i2c: ismt: Separate I2C block read from SMBus block read

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pontus Andersson <epontan@...il.com>

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.

Fixes: b6c159a9cb69 ("i2c: ismt: Don't duplicate the receive length for block reads")
Signed-off-by: Pontus Andersson <epontan@...il.com>
Tested-by: Stephen Douthit <stephend@...engineering.com>
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/i2c/busses/i2c-ismt.c
+++ b/drivers/i2c/busses/i2c-ismt.c
@@ -338,12 +338,15 @@ 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;
 	}