Re: [PATCH 0/3] i2c: xiic: fix SMBus block read and PEC support

[Michal Simek <michal.simek@amd.com>]

On 6/9/26 16:26, Shubhrajyoti Datta wrote:
> On Tue, Apr 28, 2026 at 5:48 AM Abdurrahman Hussain via B4 Relay
> <devnull+abdurrahman.nexthop.ai@kernel.org> wrote:
>>
>> This series fixes three independent bugs in the Xilinx AXI IIC driver
>> that together make SMBus block reads with PEC return -EBADMSG or -EIO
>> on otherwise clean transfers. They only surface when the client has
>> I2C_CLIENT_PEC set; non-PEC block reads happen to mask each issue in
>> turn.
>>
>> The problems were uncovered driving an adm1266 PMBus device behind a
>> Xilinx AXI IIC FPGA block and reading its 64-byte blackbox record.
>>
>> Patch 1 stops xiic_smbus_block_read_setup() from truncating rx_msg->len.
>> The i2c core appends a byte to msg->len when PEC is enabled, so
>> overwriting the length to "block size + 1" silently drops the PEC byte
>> and i2c_smbus_check_pec() then reads the last payload byte as the PEC.
>>
>> Patch 2 raises the RX_FULL threshold so the interrupt only fires once
>> every remaining byte (payload plus optional PEC) is already buffered in
>> the FIFO. The previous threshold of rxmsg_len - 2 caused the
>> bytes_rem == 1 path in xiic_read_rx() to NACK a byte still on the wire.
>>
>> Patch 3 stops the BNB handler from forcing tx_msg->len = 1 to signal
>> completion. tx_msg and rx_msg alias the same i2c_msg during a receive,
>> so this also clobbered rx_msg->len; and because tx_pos is already at 2
>> in the PEC case, the unsigned subtraction in xiic_tx_space() underflowed
>> and the STATE_DONE check fell through to STATE_ERROR. Advancing tx_pos
>> up to msg->len drives tx_space to zero without touching the length.
>>
>> All three patches are pure bug fixes; non-PEC behaviour is unchanged.
>> Tested on real hardware -- a Xilinx AXI IIC controller talking to an
>> adm1266, where 64-byte PEC-checked block reads now complete cleanly.
>>
>> Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
> 
> LGTM
> Reviewed-by: Shubhrajyoti Datta <shubhrajyoti.datta@amd.com>

Acked-by: Michal Simek <michal.simek@amd.com>

Thanks,
Michal