Digging deeper into how that MCU behaves, I found out it can return
more status codes than the "@0" for "ok".

The additional codes can report a failed checksum verification and
some "general" error for the command execution.

This also explains sporadic command timeout messages, I have seen
over time, when the controller sends an error code while we expect
a longer reply from it.

So while I'm not sure yet why it reports an error, with these changes
we at least handle the error return code in a meaningful way.


Heiko Stuebner (4):
  mfd: qnap-mcu: Calculate the checksum on the actual number of bytes
    received
  mfd: qnap-mcu: Use EPROTO in stead of EIO on checksum errors
  mfd: qnap-mcu: Move checksum verification to its own function
  mfd: qnap-mcu: Add proper error handling for command errors

 drivers/mfd/qnap-mcu.c | 55 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 4 deletions(-)

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2.47.2