rapidio/tsi721_dma: rework scatter-gather list handling

Rework Tsi721 RapidIO DMA engine support to allow handling data
scatter/gather lists longer than number of hardware buffer descriptors in
the DMA channel's descriptor list.

The current implementation of Tsi721 DMA transfers requires that number of
entries in a scatter/gather list provided by a caller of
dmaengine_prep_rio_sg() should not exceed number of allocated hardware
buffer descriptors.

This patch removes the limitation by processing long scatter/gather lists
by sections that can be transferred using hardware descriptor ring of
configured size.  It also introduces a module parameter
"dma_desc_per_channel" to allow run-time configuration of Tsi721 hardware
buffer descriptor rings.

Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Andre van Herk <andre.van.herk@prodrive-technologies.com>
Cc: Stef van Os <stef.van.os@prodrive-technologies.com>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rapidio/devices/tsi721.h

@@ -644,27 +644,26 @@ enum tsi721_smsg_int_flag {
 
 #ifdef CONFIG_RAPIDIO_DMA_ENGINE
 
-#define TSI721_BDMA_BD_RING_SZ	128
 #define TSI721_BDMA_MAX_BCOUNT	(TSI721_DMAD_BCOUNT1 + 1)
 
 struct tsi721_tx_desc {
 	struct dma_async_tx_descriptor	txd;
-	struct tsi721_dma_desc		*hw_desc;
 	u16				destid;
 	/* low 64-bits of 66-bit RIO address */
 	u64				rio_addr;
 	/* upper 2-bits of 66-bit RIO address */
 	u8				rio_addr_u;
-	u32				bcount;
-	bool				interrupt;
+	enum dma_rtype			rtype;
 	struct list_head		desc_node;
-	struct list_head		tx_list;
+	struct scatterlist		*sg;
+	unsigned int			sg_len;
+	enum dma_status			status;
 };
 
 struct tsi721_bdma_chan {
 	int		id;
 	void __iomem	*regs;
-	int		bd_num;		/* number of buffer descriptors */
+	int		bd_num;		/* number of HW buffer descriptors */
 	void		*bd_base;	/* start of DMA descriptors */
 	dma_addr_t	bd_phys;
 	void		*sts_base;	/* start of DMA BD status FIFO */
@@ -680,7 +679,6 @@ struct tsi721_bdma_chan {
 	struct list_head	active_list;
 	struct list_head	queue;
 	struct list_head	free_list;
-	dma_cookie_t		completed_cookie;
 	struct tasklet_struct	tasklet;
 	bool			active;
 };