mmc: mmc_rescan detects card change in one run

With this patch, mmc_rescan can detect the removal of an mmc card and
the insertion of (possibly another) card in the same run. This means
that a card change can be detected without having to call
mmc_detect_change multiple times.

This change generalises the core such that it can be easily used by
hosts which provide a mechanism to detect only the presence of a card
reader cover, which has to be taken off in order to insert a card. Other
hosts ("card detect" or "MMC_CAP_NEEDS_POLL") each receive an event when
a card is removed and when a card is inserted, so it is sufficient for
them if mmc_rescan handles only one event at a time. "Cover detect"
hosts, however, only receive events about the cover status. This means
that between 2 subsequent events, both a card removal and a card
insertion can occur. In this case, the pre-patch version of mmc_rescan
would only detect the removal of the previous card but not the insertion
of the new card.
Signed-off-by: Jorg Schummer <ext-jorg.2.schummer@nokia.com>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>

drivers/mmc/core/core.c

@@ -855,7 +855,23 @@ void mmc_rescan(struct work_struct *work)
 
 	mmc_bus_get(host);
 
-	if (host->bus_ops == NULL) {
+	/* if there is a card registered, check whether it is still present */
+	if ((host->bus_ops != NULL) && host->bus_ops->detect && !host->bus_dead)
+		host->bus_ops->detect(host);
+
+	mmc_bus_put(host);
+
+
+	mmc_bus_get(host);
+
+	/* if there still is a card present, stop here */
+	if (host->bus_ops != NULL) {
+		mmc_bus_put(host);
+		goto out;
+	}
+
+	/* detect a newly inserted card */
+
 	/*
 	 * Only we can add a new handler, so it's safe to
 	 * release the lock here.
@@ -904,12 +920,7 @@ void mmc_rescan(struct work_struct *work)
 
 	mmc_release_host(host);
 	mmc_power_off(host);
-	} else {
-		if (host->bus_ops->detect && !host->bus_dead)
-			host->bus_ops->detect(host);
 
-		mmc_bus_put(host);
-	}
 out:
 	if (host->caps & MMC_CAP_NEEDS_POLL)
 		mmc_schedule_delayed_work(&host->detect, HZ);