mmc: make number of mmcblk minors configurable

The old limit of number of minor numbers per mmcblk device was hardcoded
at 8.  This isn't enough for some of the more elaborate partitioning
schemes, for example those used by Chrome OS.

Since there might be a bunch of systems out there with static /dev
contents that relies on the old numbering scheme, let's make it a
build-time option with the default set to the previous 8.

Also provide a boot/modprobe-time parameter to override the config
default: mmcblk.perdev_minors.

Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: Mandeep Baines <msb@chromium.org>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Andrew Chew <achew@nvidia.com>
Change-Id: I86de89c4fae878f077743f58127cc8afa0c58f2a
Reviewed-on: http://git-master/r/53023
Reviewed-by: Allen Martin <amartin@nvidia.com>

3 files changed, 53 insertions, 10 deletions

diff --git a/Documentation/devices.txt b/Documentation/devices.txt
index d0d1df6cb5de..dd5768d706d3 100644
--- a/Documentation/devices.txt
+++ b/Documentation/devices.txt
@@ -2519,6 +2519,12 @@ Your cooperation is appreciated.
 		  8 = /dev/mmcblk1      Second SD/MMC card
 		    ...
 
+		The start of next SD/MMC card can be configured with
+		CONFIG_MMC_BLOCK_MINORS, or overridden at boot/modprobe
+		time using the mmcblk.perdev_minors option. That would
+		bump the offset between each card to be the configured
+		value instead of the default 8.
+
 179 char	CCube DVXChip-based PCI products
 		  0 = /dev/dvxirq0	First DVX device
 		  1 = /dev/dvxirq1	Second DVX device
diff --git a/drivers/mmc/card/Kconfig b/drivers/mmc/card/Kconfig
index 86948f90c3ff..cc9d7e77c254 100644
--- a/drivers/mmc/card/Kconfig
+++ b/drivers/mmc/card/Kconfig
@@ -14,6 +14,23 @@ config MMC_BLOCK
 	  mount the filesystem. Almost everyone wishing MMC support
 	  should say Y or M here.
 
+config MMC_BLOCK_MINORS
+	int "Number of minors per block device"
+	range 4 256
+	default 8
+	help
+	  Number of minors per block device. One is needed for every
+	  partition on the disk (plus one for the whole disk).
+
+	  Number of total MMC minors available is 256, so your number
+	  of supported block devices will be limited to 256 divided
+	  by this number.
+
+	  Default is 8 to be backwards compatible with previous
+	  hardwired device numbering.
+
+	  If unsure, say 8 here.
+
 config MMC_BLOCK_BOUNCE
 	bool "Use bounce buffer for simple hosts"
 	depends on MMC_BLOCK
diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index e6f74718e06f..0359c09ca5c2 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -44,6 +44,12 @@
 #include "queue.h"
 
 MODULE_ALIAS("mmc:block");
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "mmcblk."
+
+static DEFINE_MUTEX(block_mutex);
 
 #define INAND_CMD38_ARG_EXT_CSD  113
 #define INAND_CMD38_ARG_ERASE    0x00
@@ -53,12 +59,19 @@ MODULE_ALIAS("mmc:block");
 #define INAND_CMD38_ARG_SECTRIM2 0x88
 
 /*
- * max 8 partitions per card
+ * The defaults come from config options but can be overriden by module
+ * or bootarg options.
+ */
+static int perdev_minors = CONFIG_MMC_BLOCK_MINORS;
+
+/*
+ * We've only got one major, so number of mmcblk devices is
+ * limited to 256 / number of minors per device.
  */
-#define MMC_SHIFT	3
-#define MMC_NUM_MINORS	(256 >> MMC_SHIFT)
+static int max_devices;
 
-static DECLARE_BITMAP(dev_use, MMC_NUM_MINORS);
+/* 256 minors, so at most 256 separate devices */
+static DECLARE_BITMAP(dev_use, 256);
 
 /*
  * There is one mmc_blk_data per slot.
@@ -74,6 +87,9 @@ struct mmc_blk_data {
 
 static DEFINE_MUTEX(open_lock);
 
+module_param(perdev_minors, int, 0444);
+MODULE_PARM_DESC(perdev_minors, "Minors numbers to allocate per device");
+
 static struct mmc_blk_data *mmc_blk_get(struct gendisk *disk)
 {
 	struct mmc_blk_data *md;
@@ -94,7 +110,7 @@ static void mmc_blk_put(struct mmc_blk_data *md)
 	mutex_lock(&open_lock);
 	md->usage--;
 	if (md->usage == 0) {
-		int devidx = md->disk->first_minor >> MMC_SHIFT;
+		int devidx = md->disk->first_minor / perdev_minors;
 
 		blk_cleanup_queue(md->queue.queue);
 
@@ -611,8 +627,8 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
 	struct mmc_blk_data *md;
 	int devidx, ret;
 
-	devidx = find_first_zero_bit(dev_use, MMC_NUM_MINORS);
-	if (devidx >= MMC_NUM_MINORS)
+	devidx = find_first_zero_bit(dev_use, max_devices);
+	if (devidx >= max_devices)
 		return ERR_PTR(-ENOSPC);
 	__set_bit(devidx, dev_use);
 
@@ -629,7 +645,7 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
 	 */
 	md->read_only = mmc_blk_readonly(card);
 
-	md->disk = alloc_disk(1 << MMC_SHIFT);
+	md->disk = alloc_disk(perdev_minors);
 	if (md->disk == NULL) {
 		ret = -ENOMEM;
 		goto err_kfree;
@@ -646,7 +662,7 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
 	md->queue.data = md;
 
 	md->disk->major	= MMC_BLOCK_MAJOR;
-	md->disk->first_minor = devidx << MMC_SHIFT;
+	md->disk->first_minor = devidx * perdev_minors;
 	md->disk->fops = &mmc_bdops;
 	md->disk->private_data = md;
 	md->disk->queue = md->queue.queue;
@@ -730,7 +746,6 @@ static int mmc_blk_probe(struct mmc_card *card)
 {
 	struct mmc_blk_data *md;
 	int err;
-
 	char cap_str[10];
 
 	/*
@@ -830,6 +845,11 @@ static int __init mmc_blk_init(void)
 {
 	int res;
 
+	if (perdev_minors != CONFIG_MMC_BLOCK_MINORS)
+		pr_info("mmcblk: using %d minors per device\n", perdev_minors);
+
+	max_devices = 256 / perdev_minors;
+
 	res = register_blkdev(MMC_BLOCK_MAJOR, "mmc");
 	if (res)
 		goto out;