mmc: support unsafe resume of cards

Since many have the system root on MMC/SD we must allow some foot
shooting when it comes to resume.

We cannot detect if a card is removed and reinserted during suspend,
so the safe approach would be to assume it was, avoiding potential
filesystem corruption. This will of course not work if you cannot
release the card before suspend.

This commit adds a compile time option that makes the MMC layer
assume the card wasn't touched if it is redetected upon resume.

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

drivers/mmc/Kconfig

@@ -19,6 +19,8 @@ config MMC_DEBUG
 	  This is an option for use by developers; most people should
 	  say N here.  This enables MMC core and driver debugging.
 
+source "drivers/mmc/core/Kconfig"
+
 source "drivers/mmc/card/Kconfig"
 
 source "drivers/mmc/host/Kconfig"

drivers/mmc/core/Kconfig

@@ -0,0 +1,17 @@
+#
+# MMC core configuration
+#
+
+config MMC_UNSAFE_RESUME
+	bool "Allow unsafe resume (DANGEROUS)"
+	depends on MMC != n
+	help
+	  If you say Y here, the MMC layer will assume that all cards
+	  stayed in their respective slots during the suspend. The
+	  normal behaviour is to remove them at suspend and
+	  redetecting them at resume. Breaking this assumption will
+	  in most cases result in data corruption.
+
+	  This option is usually just for embedded systems which use
+	  a MMC/SD card for rootfs. Most people should say N here.
+

drivers/mmc/core/core.c

@@ -677,14 +677,19 @@ int mmc_suspend_host(struct mmc_host *host, pm_message_t state)
 
 	mmc_bus_get(host);
 	if (host->bus_ops && !host->bus_dead) {
-		if (host->bus_ops->remove)
-			host->bus_ops->remove(host);
-		mmc_detach_bus(host);
+		if (host->bus_ops->suspend)
+			host->bus_ops->suspend(host);
+		if (!host->bus_ops->resume) {
+			if (host->bus_ops->remove)
+				host->bus_ops->remove(host);
+
+			mmc_claim_host(host);
+			mmc_detach_bus(host);
+			mmc_release_host(host);
+		}
 	}
 	mmc_bus_put(host);
 
-	BUG_ON(host->card);
-
 	mmc_power_off(host);
 
 	return 0;
@@ -698,7 +703,19 @@ EXPORT_SYMBOL(mmc_suspend_host);
  */
 int mmc_resume_host(struct mmc_host *host)
 {
-	mmc_rescan(&host->detect.work);
+	mmc_bus_get(host);
+	if (host->bus_ops && !host->bus_dead) {
+		mmc_power_up(host);
+		BUG_ON(!host->bus_ops->resume);
+		host->bus_ops->resume(host);
+	}
+	mmc_bus_put(host);
+
+	/*
+	 * We add a slight delay here so that resume can progress
+	 * in parallel.
+	 */
+	mmc_detect_change(host, 1);
 
 	return 0;
 }

drivers/mmc/core/core.h

@@ -18,6 +18,8 @@
 struct mmc_bus_ops {
 	void (*remove)(struct mmc_host *);
 	void (*detect)(struct mmc_host *);
+	void (*suspend)(struct mmc_host *);
+	void (*resume)(struct mmc_host *);
 };
 
 void mmc_attach_bus(struct mmc_host *host, const struct mmc_bus_ops *ops);