[RFC][PATCH v2] mmc_block: Allow more than 8 partitions per card

[John Stultz <john.stultz@linaro.org>]

From: Colin Cross <ccross@android.com>

It is quite common for Android devices to utilize more
then 8 partitions on internal eMMC storage.

The vanilla kernel can support this via
CONFIG_MMC_BLOCK_MINORS, however that solution caps the
system to 256 minors total, which limits the number of
mmc cards the system can support.

This patch, which has been carried for quite awhile in
the AOSP common tree, provides an alternative solution
that doesn't seem to limit the total card count. So I
wanted to submit it for consideration upstream.

This patch sets the GENHD_FL_EXT_DEVT flag, which will
allocate minor number in major 259 for partitions past
disk->minors.

It also removes the use of disk_devt to determine devidx
from md->disk. md->disk->first_minor is always initialized
from devidx and can always be used to recover it.

Thoughts or feedback would be greatly appreciated.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Chuanxiao Dong <chuanxiao.dong@intel.com>
Cc: Shawn Lin <shawn.lin@rock-chips.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Android Kernel Team <kernel-team@android.com>
Cc: linux-mmc@vger.kernel.org
Signed-off-by: Colin Cross <ccross@android.com>
[jstultz: Added context to commit message]
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
v2: Added context to commit message about CONFIG_MMC_BLOCK_MINORS
    and its limitations.

 drivers/mmc/card/block.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index c742cfd..564436e 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -172,11 +172,7 @@ static struct mmc_blk_data *mmc_blk_get(struct gendisk *disk)
 
 static inline int mmc_get_devidx(struct gendisk *disk)
 {
-	int devmaj = MAJOR(disk_devt(disk));
-	int devidx = MINOR(disk_devt(disk)) / perdev_minors;
-
-	if (!devmaj)
-		devidx = disk->first_minor / perdev_minors;
+	int devidx = disk->first_minor / perdev_minors;
 	return devidx;
 }
 
@@ -2162,6 +2158,7 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
 	md->disk->queue = md->queue.queue;
 	md->disk->driverfs_dev = parent;
 	set_disk_ro(md->disk, md->read_only || default_ro);
+	md->disk->flags = GENHD_FL_EXT_DEVT;
 	if (area_type & (MMC_BLK_DATA_AREA_RPMB | MMC_BLK_DATA_AREA_BOOT))
 		md->disk->flags |= GENHD_FL_NO_PART_SCAN;
 
-- 
1.9.1