dmaengine: Mark struct dma_slave_caps kernel-doc correctly, clarify

struct dma_slave_caps documentation omitted the correct kernel-doc
opening comment mark.

Document byte granularity and interpretation of the src/dst_addr_widths
bit flag fields used by struct dma_slave_caps and struct dma_device.

Add punctuation to their "directions" member documentations, and cleanup
wording of the description.
Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

include/linux/dmaengine.h

@@ -404,14 +404,16 @@ enum dma_residue_granularity {
 	DMA_RESIDUE_GRANULARITY_BURST = 2,
 };
 
-/* struct dma_slave_caps - expose capabilities of a slave channel only
- *
- * @src_addr_widths: bit mask of src addr widths the channel supports
- * @dst_addr_widths: bit mask of dstn addr widths the channel supports
- * @directions: bit mask of slave direction the channel supported
- * 	since the enum dma_transfer_direction is not defined as bits for each
- * 	type of direction, the dma controller should fill (1 << <TYPE>) and same
- * 	should be checked by controller as well
+/**
+ * struct dma_slave_caps - expose capabilities of a slave channel only
+ * @src_addr_widths: bit mask of src addr widths the channel supports.
+ *	Width is specified in bytes, e.g. for a channel supporting
+ *	a width of 4 the mask should have BIT(4) set.
+ * @dst_addr_widths: bit mask of dst addr widths the channel supports
+ * @directions: bit mask of slave directions the channel supports.
+ *	Since the enum dma_transfer_direction is not defined as bit flag for
+ *	each type, the dma controller should set BIT(<TYPE>) and same
+ *	should be checked by controller as well
  * @max_burst: max burst capability per-transfer
  * @cmd_pause: true, if pause and thereby resume is supported
  * @cmd_terminate: true, if terminate cmd is supported
@@ -678,11 +680,13 @@ struct dma_filter {
  * @dev_id: unique device ID
  * @dev: struct device reference for dma mapping api
  * @src_addr_widths: bit mask of src addr widths the device supports
+ *	Width is specified in bytes, e.g. for a device supporting
+ *	a width of 4 the mask should have BIT(4) set.
  * @dst_addr_widths: bit mask of dst addr widths the device supports
- * @directions: bit mask of slave direction the device supports since
- * 	the enum dma_transfer_direction is not defined as bits for
- * 	each type of direction, the dma controller should fill (1 <<
- * 	<TYPE>) and same should be checked by controller as well
+ * @directions: bit mask of slave directions the device supports.
+ *	Since the enum dma_transfer_direction is not defined as bit flag for
+ *	each type, the dma controller should set BIT(<TYPE>) and same
+ *	should be checked by controller as well
  * @max_burst: max burst capability per-transfer
  * @residue_granularity: granularity of the transfer residue reported
  *	by tx_status