mmc: add bus handler

Delegate protocol handling to "bus handlers". This allows the core to
just handle the task of arbitrating the bus. Initialisation and
pampering of cards is now done by the different bus handlers.

This design also allows MMC and SD (and later SDIO) to be more cleanly
separated, allowing easier maintenance.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

include/linux/mmc/host.h

@@ -131,6 +131,8 @@ struct mmc_host {
 	unsigned int		max_blk_count;	/* maximum number of blocks in one req */
 
 	/* private data */
+	spinlock_t		lock;		/* lock for claim and bus ops */
+
 	struct mmc_ios		ios;		/* current io bus settings */
 	u32			ocr;		/* the current OCR setting */
 
@@ -141,7 +143,6 @@ struct mmc_host {
 	struct mmc_card		*card;		/* device attached to this host */
 
 	wait_queue_head_t	wq;
-	spinlock_t		lock;		/* claimed lock */
 	unsigned int		claimed:1;	/* host exclusively claimed */
 
 	struct delayed_work	detect;
@@ -149,6 +150,10 @@ struct mmc_host {
 	unsigned int		removed:1;	/* host is being removed */
 #endif
 
+	const struct mmc_bus_ops *bus_ops;	/* current bus driver */
+	unsigned int		bus_refs;	/* reference counter */
+	unsigned int		bus_dead:1;	/* bus has been released */
+
 	unsigned long		private[0] ____cacheline_aligned;
 };