[PATCH] mmc: block: Use the mmc host device index as the mmcblk device index

From: Ulf Hansson
Date: Thu Apr 07 2016 - 03:58:03 EST

Commit 520bd7a8b415 ("mmc: core: Optimize boot time by detecting cards
simultaneously") causes regressions for some platforms.

These platforms relies on fixed mmcblk device indexes, instead of
deploying the defacto standard with UUID/PARTUUID. In other words their
rootfs needs to be available at hardcoded paths, like /dev/mmcblk0p2.

Such guarantees have never been made by the kernel, but clearly the above
commit changes the behaviour. More precisely, because of that the order
changes of how cards becomes detected, so do their corresponding mmcblk
device indexes.

As the above commit significantly improves boot time for some platforms
(magnitude of seconds), let's avoid reverting this change but instead
restore the behaviour of how mmcblk device indexes becomes picked.

By using the same index for the mmcblk device as for the corresponding mmc
host device, the probe order of mmc host devices decides the index we get
for the mmcblk device.

For those platforms that suffers from a regression, one could expect that
this updated behaviour should be sufficient to meet their expectations of
"fixed" mmcblk device indexes.

Another side effect from this change, is that the same index is used for
the mmc host device, the mmcblk device and the mmc block queue. That
should clarify their relationship.

Reported-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Reported-by: Laszlo Fiat <laszlo.fiat@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Fixes: 520bd7a8b415 ("mmc: core: Optimize boot time by detecting cards
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
drivers/mmc/card/block.c | 18 +-----------------
1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 3bdbe50..8a0147d 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -86,7 +86,6 @@ static int max_devices;

/* TODO: Replace these with struct ida */
-static DECLARE_BITMAP(name_use, MAX_DEVICES);

* There is one mmc_blk_data per slot.
@@ -105,7 +104,6 @@ struct mmc_blk_data {
unsigned int usage;
unsigned int read_only;
unsigned int part_type;
- unsigned int name_idx;
unsigned int reset_done;
#define MMC_BLK_READ BIT(0)
#define MMC_BLK_WRITE BIT(1)
@@ -2202,19 +2200,6 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
goto out;

- /*
- * !subname implies we are creating main mmc_blk_data that will be
- * associated with mmc_card with dev_set_drvdata. Due to device
- * partitions, devidx will not coincide with a per-physical card
- * index anymore so we keep track of a name index.
- */
- if (!subname) {
- md->name_idx = find_first_zero_bit(name_use, max_devices);
- __set_bit(md->name_idx, name_use);
- } else
- md->name_idx = ((struct mmc_blk_data *)
- dev_to_disk(parent)->private_data)->name_idx;
md->area_type = area_type;

@@ -2264,7 +2249,7 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,

snprintf(md->disk->disk_name, sizeof(md->disk->disk_name),
- "mmcblk%u%s", md->name_idx, subname ? subname : "");
+ "mmcblk%u%s", card->host->index, subname ? subname : "");

if (mmc_card_mmc(card))
@@ -2418,7 +2403,6 @@ static void mmc_blk_remove_parts(struct mmc_card *card,
struct list_head *pos, *q;
struct mmc_blk_data *part_md;

- __clear_bit(md->name_idx, name_use);
list_for_each_safe(pos, q, &md->part) {
part_md = list_entry(pos, struct mmc_blk_data, part);