spi: bcm2835: Synchronize with callback on DMA termination

Commit b36f09c3c441 ("dmaengine: Add transfer termination
synchronization support") deprecated dmaengine_terminate_all() in favor
of dmaengine_terminate_sync() and dmaengine_terminate_async() to avoid
freeing resources used by the DMA callback before its execution has
concluded.

Commit de92436ac40f ("dmaengine: bcm2835-dma: Use vchan_terminate_vdesc()
instead of desc_free") amended the BCM2835 DMA driver with an
implementation of ->device_synchronize(), which is a prerequisite for
dmaengine_terminate_sync().  Thus, clients of the DMA driver (such as
the BCM2835 SPI driver) may now be converted to the new API.

It is generally desirable to use the _sync() variant except in atomic
context.  There is only a single occurrence where the BCM2835 SPI driver
calls dmaengine_terminate_all() in atomic context and that is in
bcm2835_spi_dma_done() (the RX DMA channel's callback) to terminate the
TX DMA channel.  The TX DMA channel doesn't have a callback (yet), hence
it is safe to use the _async() variant there.

Signed-off-by: Lukas Wunner <[email protected]>
Cc: Frank Pavlic <[email protected]>
Cc: Martin Sperl <[email protected]>
Cc: Noralf Trønnes <[email protected]>
Cc: Vinod Koul <[email protected]>
Signed-off-by: Mark Brown <[email protected]>

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