i2c: xiic: don't clobber msg->len to signal block-read completion

At the end of a SMBus block read the BNB handler force-set
tx_msg->len = 1 to push xiic_tx_space() to zero so the STATE_DONE
branch would fire. Two problems:

1. tx_msg and rx_msg alias the same i2c_msg struct during a receive
   (see xiic_start_recv), so overwriting tx_msg->len also changes
   rx_msg->len. The i2c core's i2c_smbus_check_pec() then reads the
   PEC from the wrong offset -- buf[0] instead of buf[rxmsg_len + 1]
   -- and either mis-validates or returns -EBADMSG.

2. xiic_start_recv sets tx_pos = msg->len (typically 2 when PEC is
   enabled). xiic_tx_space() is unsigned msg->len - tx_pos, so
   setting msg->len = 1 with tx_pos = 2 underflows to 0xFFFFFFFF and
   xiic_tx_space() never compares equal to 0 -- the STATE_DONE check
   falls through to STATE_ERROR, giving -EIO.

Instead, advance tx_pos up to msg->len. That drives tx_space to 0
without touching msg->len, preserving the buffer length that
xiic_smbus_block_read_setup() already grew to cover the length byte,
the payload and the optional PEC byte.

Fixes: e4c1ff772e1a ("i2c: xiic: Add smbus_block_read functionality")
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
Cc: <stable@vger.kernel.org> # v6.3+
Acked-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Shubhrajyoti Datta <shubhrajyoti.datta@amd.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://patch.msgid.link/20260924-i2c-xiic-v7-3-df7e752332ef@nexthop.ai

0 files changed, 0 insertions, 0 deletions