mmc: allow host claim / release nesting

This change allows the MMC host to be claimed in situations where the host
may or may not have already been claimed.  Also 'mmc_try_claim_host()' is
now exported.

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Acked-by: Matt Fleming <matt@console-pimps.org>
Cc: Ian Molton <ian@mnementh.co.uk>
Cc: "Roberto A. Foglietta" <roberto.foglietta@gmail.com>
Cc: Jarkko Lavinen <jarkko.lavinen@nokia.com>
Cc: Denis Karpov <ext-denis.2.karpov@nokia.com>
Cc: Pierre Ossman <pierre@ossman.eu>
Cc: Philip Langdale <philipl@overt.org>
Cc: "Madhusudhan" <madhu.cr@ti.com>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 338a9b3..631a2fe 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -182,6 +182,8 @@
 	struct mmc_card		*card;		/* device attached to this host */
 
 	wait_queue_head_t	wq;
+	struct task_struct	*claimer;	/* task that has host claimed */
+	int			claim_cnt;	/* "claim" nesting count */
 
 	struct delayed_work	detect;