spi: SAM add RTIO support

Implements the SPI RTIO API. Refactors many of the internal transfer
functions to work on simple types to allow for both the RTIO and existing
SPI API functions to co-exist.

Removes the unneeded shift_master specialization. Either a polling or DMA
transfer flow is used when used with RTIO as all operations are normalized.

When SPI_RTIO is enabled the spi_transceive blocking call translates
the request into an RTIO transaction placed in the queue of transactions
the device is meant to do.

Signed-off-by: Tom Burdick <[email protected]>

Author: teburd

drivers/spi/Kconfig.sam

@@ -19,4 +19,19 @@ config SPI_SAM_DMA
 	help
 	  Enable using DMA with SPI for SPI instances that enable dma channels in
 	  their device tree node.
+
+if SPI_RTIO
+config SPI_SAM_RTIO_SQ_SIZE
+	int "Number of avialable submission queue entries"
+	default 8 # Sensible default that covers most common spi transactions
+	help
+	  When RTIO is use with SPI each driver holds a context with which blocking
+	  API calls use to perform SPI transactions. This queue needs to be as deep
+	  as the longest set of spi_buf_sets used, where normal SPI operations are
+	  used (equal length buffers). It may need to be slightly deeper where the
+	  spi buffer sets for transmit/receive are not always matched equally in
+	  length as these are transformed into normal transceives.
+
+endif # SPI_RTIO
+
 endif # SPI_SAM