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

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@gmail.com>
Tested-by: Stephen Douthit <stephend@adiengineering.com>
Cc: stable@vger.kernel.org
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --git a/drivers/i2c/busses/i2c-ismt.c b/drivers/i2c/busses/i2c-ismt.c
index 22ffcb73c185f592d8b4e6bdbb1ede45cbeb4951..b51adffa484109efb842bbe75afec593ac8a1731 100644 (file)
--- a/drivers/i2c/busses/i2c-ismt.c
+++ b/drivers/i2c/busses/i2c-ismt.c
@@ -340,12 +340,15 @@ static int ismt_process_desc(const struct ismt_desc *desc,
                        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;
        }