i2c: ismt: Don't duplicate the receive length for block reads

According to Table 15-14 of the C2000 EDS (Intel doc #510524) the
rx data pointed to by the descriptor dptr contains the byte count.

desc->rxbytes reports all bytes read on the wire, including the
"byte count" byte.  So if a device sends 4 bytes in response to a
block read, on the wire and in the DMA buffer we see:

count data1 data2 data3 data4
 0x04  0xde  0xad  0xbe  0xef

That's what we want to return in data->block to the next level.

Instead we were actually prefixing that with desc->rxbytes:

bad
count count data1 data2 data3 data4
 0x05  0x04  0xde  0xad  0xbe  0xef

This was discovered while developing a BMC solution relying on the
ipmi_ssif.c driver which was trying to interpret the bogus length
field as part of the IPMI response.

Signed-off-by: Stephen Douthit <stephend@adiengineering.com>
Tested-by: Dan Priamo <danp@adiengineering.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org

diff --git a/drivers/i2c/busses/i2c-ismt.c b/drivers/i2c/busses/i2c-ismt.c
index e98e44e584a44a6e17dc3af00ae1f02ce50ae95b..9af2337eb17a00f358b6386226c74260a852e1b0 100644 (file)
--- a/drivers/i2c/busses/i2c-ismt.c
+++ b/drivers/i2c/busses/i2c-ismt.c
@@ -341,8 +341,8 @@ static int ismt_process_desc(const struct ismt_desc *desc,
                        break;
                case I2C_SMBUS_BLOCK_DATA:
                case I2C_SMBUS_I2C_BLOCK_DATA:
-                       memcpy(&data->block[1], dma_buffer, desc->rxbytes);
-                       data->block[0] = desc->rxbytes;
+                       memcpy(data->block, dma_buffer, desc->rxbytes);
+                       data->block[0] = desc->rxbytes - 1;
                        break;
                }
                return 0;