From: Mike Snitzer <[email-masked]>

Allow discards even if the pool's block size is not a power of 2.
The block layer assumes discard_granularity is a power of 2, so changes
are needed to allow discards when a pool is using a block size that is
not a power of 2.  Otherwise the math in blkdev_issue_discard will not
work.

This patch depends on commit c6e666345e1b79c62b ("block: split discard
into aligned requests") to ensure properly aligned discard requests are
issued to thinp.

Signed-off-by: Mike Snitzer <[email-masked]>
Signed-off-by: Joe Thornber <[email-masked]>

---
 drivers/md/dm-thin.c |   24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

Index: linux/drivers/md/dm-thin.c
===================================================================
--- linux.orig/drivers/md/dm-thin.c
+++ linux/drivers/md/dm-thin.c
@@ -2272,15 +2272,6 @@ static int pool_ctr(struct dm_target *ti
 		goto out_flags_changed;
 	}
 
-	/*
-	 * The block layer requires discard_granularity to be a power of 2.
-	 */
-	if (pf.discard_enabled && !is_power_of_2(block_size)) {
-		ti->error = "Discard support must be disabled when the block size is not a power of 2";
-		r = -EINVAL;
-		goto out_flags_changed;
-	}
-
 	pt->pool = pool;
 	pt->ti = ti;
 	pt->metadata_dev = metadata_dev;
@@ -2762,6 +2753,11 @@ static int pool_merge(struct dm_target *
 	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
 }
 
+static bool block_size_is_power_of_two(struct pool *pool)
+{
+	return pool->sectors_per_block_shift >= 0;
+}
+
 static void set_discard_limits(struct pool_c *pt, struct queue_limits *limits)
 {
 	struct pool *pool = pt->pool;
@@ -2775,8 +2771,16 @@ static void set_discard_limits(struct po
 	if (pt->adjusted_pf.discard_passdown) {
 		data_limits = &bdev_get_queue(pt->data_dev->bdev)->limits;
 		limits->discard_granularity = data_limits->discard_granularity;
-	} else
+	} else if (block_size_is_power_of_two(pool))
 		limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
+	else
+		/*
+		 * Use largest power of 2 that is a factor of sectors_per_block
+		 * but at least DATA_DEV_BLOCK_SIZE_MIN_SECTORS.
+		 */
+		limits->discard_granularity = max(1 << (ffs(pool->sectors_per_block) - 1),
+						  DATA_DEV_BLOCK_SIZE_MIN_SECTORS) << SECTOR_SHIFT;
+
 }
 
 static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)