mailbox: mpfs: add bounded wait for BUSY to clear before sending request

The MPFS mailbox driver currently checks the BUSY bit at the start of
mpfs_mbox_send() and immediately returns -EBUSY if the controller is
busy.

On MPFS, BUSY may be transiently asserted during early boot even though
no other U-Boot service is actively executing. In Linux, returning
-EBUSY here is retryable via the mailbox framework and scheduler, but in
U-Boot this results in a hard failure.

Replace the immediate BUSY check with a bounded wait using
regmap_read_poll_timeout(), waiting for the controller to become idle
before issuing a new request. This preserves the intent of the BUSY
check while avoiding spurious early-boot failures in U-Boot’s
synchronous, polled execution model.

The timeout is conservative and based on observed MPFS behaviour, where
BUSY clears within a few milliseconds.

Signed-off-by: Jamie Gibbons <[email protected]>
Reviewed-by: Conor Dooley <[email protected]>

0 files changed, 0 insertions, 0 deletions