spi: omap2-mcspi: handle DMA setup failures

The DMA paths ignore failures from dmaengine_slave_config(), descriptor
preparation and dmaengine_submit(), and carry FIXME comments about
falling back to PIO. A failed setup can leave a half-started transfer
or wait for a completion that never arrives.

Check each step and clean up with dmaengine_terminate_sync() on error.
Prepare both descriptors before issuing either channel. Fall back to
PIO only for host-mode transfers that have a TX buffer, when no DMA has
been started and cleanup succeeded. RX-only and target-mode transfers
return the error instead, since the bus may already be clocking.

The FIFO is enabled before the DMA attempt, but the PIO path polls
per-word TXS/RXS and does not expect FIFO mode. Disable the FIFO, with
the channel off while its bits change, before falling back.

Tested on an AM642 board with a TI 6.12.57 vendor kernel built with
this patch and booted from RAM. On a McSPI bus using DMA, 200
iterations of 4096-byte TX and 1024-byte RX spidev transfers completed
with no errors, timeouts or kernel warnings. With a temporary change
that fails every DMA-sized TX setup, 60 spidev writes fell back to PIO
with no errors or timeouts. That test used a bus with no device
attached and did not show a difference with and without the FIFO
disable, which is based on reading the code.

Fixes: 53741ed8f0a3 ("spi: omap2-mcspi: add DMA engine support")
Link: https://lore.kernel.org/r/20250914022132.319227-1-alex.t.tran@gmail.com
Signed-off-by: Sahaj Chaudhari <sahaj123.sc@gmail.com>
Link: https://patch.msgid.link/20261015064341.1100422-1-sahaj123.sc@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

0 files changed, 0 insertions, 0 deletions