From 840d8acc87925deb3c75566fde9ca81d2f47f98c Mon Sep 17 00:00:00 2001 From: Abdurrahman Hussain Date: Thu, 24 Sep 2026 17:10:37 -0700 Subject: 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 Cc: # v6.3+ Acked-by: Michal Simek Reviewed-by: Shubhrajyoti Datta Signed-off-by: Andi Shyti Link: https://patch.msgid.link/20260924-i2c-xiic-v7-3-df7e752332ef@nexthop.ai --- drivers/i2c/busses/i2c-xiic.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c index 5cd737c76..5e397a7e6 100644 --- a/drivers/i2c/busses/i2c-xiic.c +++ b/drivers/i2c/busses/i2c-xiic.c @@ -889,8 +889,11 @@ static irqreturn_t xiic_process(int irq, void *dev_id) if (i2c->tx_msg && i2c->smbus_block_read) { i2c->smbus_block_read = false; - /* Set requested message len=1 to indicate STATE_DONE */ - i2c->tx_msg->len = 1; + /* + * Drive xiic_tx_space() to 0 to signal STATE_DONE + * without truncating the rx_msg length. + */ + i2c->tx_pos = i2c->tx_msg->len; } if (!i2c->tx_msg) -- cgit v1.3.1