mailbox: axiado: fix RX frame draining and error handling

Two RX-path bugs found during bring-up:

1. axiado_rx_thread() previously consumed only one frame per
   invocation. Multiple frames can accumulate in the FIFO while the
   threaded handler is running. Split the single-frame handling into
   axiado_mbox_receive_one_frame() and drain all currently queued
   frames before returning from the handler. A cond_resched() in the
   drain loop prevents a continuously-fed channel from monopolizing
   the CPU.

2. readl_poll_timeout() waiting for the remainder of a frame can
   return success either because the required FIFO level was reached
   or because a FIFO error appeared -- it does not distinguish the
   two. The old code did not check for that case and could therefore
   enter the read loop without enough words actually being present.
   Explicitly inspect the error status after the poll: if an error
   occurs while waiting for the remainder of an already-started
   frame, treat that frame as unusable and flush the FIFO to
   resynchronize, rather than risk delivering incomplete or garbage
   data to the client.

While here:

 - Track whether the handler actually serviced a hardware condition,
   such as clearing a FIFO error or consuming frame data. Return
   IRQ_HANDLED whenever something was serviced, even if the FIFO is
   empty afterward, instead of reporting IRQ_NONE after handling a
   hardware condition.

 - Use readsl() for the RX FIFO payload. The destination is the
   driver-owned rx_buffer allocated by devm_kzalloc(), so it has
   suitable alignment for the stream accessor. readsl() is
   appropriate for copying a sequence of words from the FIFO into
   that buffer. The TX path intentionally stays on
   get_unaligned_le32()/writel(): its buffer is supplied by an
   external mailbox client, the mailbox API gives no guarantee that
   buffer is naturally aligned, and the TX path also explicitly
   handles a partial final word.

mbox_free_channel() invokes ->shutdown() before chan->cl is cleared,
and axiado_mbox_shutdown() calls disable_irq(), which waits for the
in-flight threaded handler to complete, so no functional change is
needed for that path.

Verified: builds clean with the aarch64 cross-compiler, passes
checkpatch.pl, and was regression-tested with live mailbox traffic on
AX3005.

Fixes: 14af7a96afa3 ("mailbox: add Axiado AX3005 mailbox driver")
Signed-off-by: Swark Yang <syang@axiado.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

0 files changed, 0 insertions, 0 deletions