mmc: add module parameter to set whether cards are assumed removable

Some people run general-purpose distribution kernels on netbooks with
a card that is physically non-removable or logically non-removable
(e.g. used for /home) and cannot be cleanly unmounted during suspend.
Add a module parameter to set whether cards are assumed removable or
non-removable, with the default set by CONFIG_MMC_UNSAFE_RESUME.

In general, it is not possible to tell whether a card present in an MMC
slot after resume is the same that was there before suspend.  So there are
two possible behaviours, each of which will cause data loss in some cases:

CONFIG_MMC_UNSAFE_RESUME=n (default): Cards are assumed to be removed
during suspend.  Any filesystem on them must be unmounted before suspend;
otherwise, buffered writes will be lost.

CONFIG_MMC_UNSAFE_RESUME=y: Cards are assumed to remain present during
suspend.  They must not be swapped during suspend; otherwise, buffered
writes will be flushed to the wrong card.

Currently the choice is made at compile time and this allows that to be
overridden at module load time.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Wouter van Heyst <larstiq@larstiq.dyndns.org>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/mmc/core/Kconfig

@@ -3,7 +3,7 @@
 #
 
 config MMC_UNSAFE_RESUME
-	bool "Allow unsafe resume (DANGEROUS)"
+	bool "Assume MMC/SD cards are non-removable (DANGEROUS)"
 	help
 	  If you say Y here, the MMC layer will assume that all cards
 	  stayed in their respective slots during the suspend. The
@@ -14,3 +14,5 @@ config MMC_UNSAFE_RESUME
 	  This option is usually just for embedded systems which use
 	  a MMC/SD card for rootfs. Most people should say N here.
 
+	  This option sets a default which can be overridden by the
+	  module parameter "removable=0" or "removable=1".

drivers/mmc/core/core.c

@@ -47,6 +47,22 @@ static struct workqueue_struct *workqueue;
 int use_spi_crc = 1;
 module_param(use_spi_crc, bool, 0);
 
+/*
+ * We normally treat cards as removed during suspend if they are not
+ * known to be on a non-removable bus, to avoid the risk of writing
+ * back data to a different card after resume.  Allow this to be
+ * overridden if necessary.
+ */
+#ifdef CONFIG_MMC_UNSAFE_RESUME
+int mmc_assume_removable;
+#else
+int mmc_assume_removable = 1;
+#endif
+module_param_named(removable, mmc_assume_removable, bool, 0644);
+MODULE_PARM_DESC(
+	removable,
+	"MMC/SD cards are removable and may be removed during suspend");
+
 /*
  * Internal function. Schedule delayed work in the MMC work queue.
  */

drivers/mmc/core/core.h

@@ -54,7 +54,9 @@ int mmc_attach_mmc(struct mmc_host *host, u32 ocr);
 int mmc_attach_sd(struct mmc_host *host, u32 ocr);
 int mmc_attach_sdio(struct mmc_host *host, u32 ocr);
 
+/* Module parameters */
 extern int use_spi_crc;
+extern int mmc_assume_removable;
 
 /* Debugfs information for hosts and cards */
 void mmc_add_host_debugfs(struct mmc_host *host);

drivers/mmc/core/mmc.c

@@ -602,25 +602,6 @@ static int mmc_awake(struct mmc_host *host)
 	return err;
 }
 
-#ifdef CONFIG_MMC_UNSAFE_RESUME
-
-static const struct mmc_bus_ops mmc_ops = {
-	.awake = mmc_awake,
-	.sleep = mmc_sleep,
-	.remove = mmc_remove,
-	.detect = mmc_detect,
-	.suspend = mmc_suspend,
-	.resume = mmc_resume,
-	.power_restore = mmc_power_restore,
-};
-
-static void mmc_attach_bus_ops(struct mmc_host *host)
-{
-	mmc_attach_bus(host, &mmc_ops);
-}
-
-#else
-
 static const struct mmc_bus_ops mmc_ops = {
 	.awake = mmc_awake,
 	.sleep = mmc_sleep,
@@ -645,15 +626,13 @@ static void mmc_attach_bus_ops(struct mmc_host *host)
 {
 	const struct mmc_bus_ops *bus_ops;
 
-	if (host->caps & MMC_CAP_NONREMOVABLE)
+	if (host->caps & MMC_CAP_NONREMOVABLE || !mmc_assume_removable)
 		bus_ops = &mmc_ops_unsafe;
 	else
 		bus_ops = &mmc_ops;
 	mmc_attach_bus(host, bus_ops);
 }
 
-#endif
-
 /*
  * Starting point for MMC card init.
  */

drivers/mmc/core/sd.c

@@ -606,23 +606,6 @@ static void mmc_sd_power_restore(struct mmc_host *host)
 	mmc_release_host(host);
 }
 
-#ifdef CONFIG_MMC_UNSAFE_RESUME
-
-static const struct mmc_bus_ops mmc_sd_ops = {
-	.remove = mmc_sd_remove,
-	.detect = mmc_sd_detect,
-	.suspend = mmc_sd_suspend,
-	.resume = mmc_sd_resume,
-	.power_restore = mmc_sd_power_restore,
-};
-
-static void mmc_sd_attach_bus_ops(struct mmc_host *host)
-{
-	mmc_attach_bus(host, &mmc_sd_ops);
-}
-
-#else
-
 static const struct mmc_bus_ops mmc_sd_ops = {
 	.remove = mmc_sd_remove,
 	.detect = mmc_sd_detect,
@@ -643,15 +626,13 @@ static void mmc_sd_attach_bus_ops(struct mmc_host *host)
 {
 	const struct mmc_bus_ops *bus_ops;
 
-	if (host->caps & MMC_CAP_NONREMOVABLE)
+	if (host->caps & MMC_CAP_NONREMOVABLE || !mmc_assume_removable)
 		bus_ops = &mmc_sd_ops_unsafe;
 	else
 		bus_ops = &mmc_sd_ops;
 	mmc_attach_bus(host, bus_ops);
 }
 
-#endif
-
 /*
  * Starting point for SD card init.
  */