mmc: core: convert slot functions to managed allocation

This prepares for the addition of further slot functions.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index c1a03ee..65c64ee 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -11,6 +11,7 @@
 #define LINUX_MMC_HOST_H
 
 #include <linux/leds.h>
+#include <linux/mutex.h>
 #include <linux/sched.h>
 #include <linux/device.h>
 #include <linux/fault-inject.h>
@@ -154,6 +155,7 @@
  * struct mmc_slot - MMC slot functions
  *
  * @cd_irq:		MMC/SD-card slot hotplug detection IRQ or -EINVAL
+ * @lock:		protect the @handler_priv pointer
  * @handler_priv:	MMC/SD-card slot context
  *
  * Some MMC/SD host controllers implement slot-functions like card and
@@ -163,6 +165,7 @@
  */
 struct mmc_slot {
 	int cd_irq;
+	struct mutex lock;
 	void *handler_priv;
 };