[PATCH v2] mtd: Avoid probe failures when mtd->dbg.dfs_dir is invalid

[Boris Brezillon]

Commit e8e3edb95ce6 ("mtd: create per-device and module-scope debugfs
entries") tried to make MTD related debugfs stuff consistent across the
MTD framework by creating a root <debugfs>/mtd/ directory containing
one directory per MTD device.

The problem is that, by default, the MTD layer only registers the
master device if no partitions are defined for this master. This
behavior breaks all drivers that expect mtd->dbg.dfs_dir to be filled
correctly after calling mtd_device_register() in order to add their own
debugfs entries.

The only way we can force all MTD masters to be registered no matter if
they expose partitions or not is by enabling the
CONFIG_MTD_PARTITIONED_MASTER option.

In such situations, there's no other solution but to accept skipping
debugfs initialization when dbg.dfs_dir is invalid, and when this
happens, inform the user that he should consider enabling
CONFIG_MTD_PARTITIONED_MASTER.

Fixes: e8e3edb95ce6 ("mtd: create per-device and module-scope debugfs entries")
Cc: <stable at vger.kernel.org>
Cc: Mario J. Rugiero <mrugiero at gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
---
 drivers/mtd/devices/docg3.c |  7 ++++++-
 drivers/mtd/nand/nandsim.c  | 13 +++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/devices/docg3.c b/drivers/mtd/devices/docg3.c
index 84b16133554b..0806f72102c0 100644
--- a/drivers/mtd/devices/docg3.c
+++ b/drivers/mtd/devices/docg3.c
@@ -1814,8 +1814,13 @@ static void __init doc_dbg_register(struct mtd_info *floor)
 	struct dentry *root = floor->dbg.dfs_dir;
 	struct docg3 *docg3 = floor->priv;
 
-	if (IS_ERR_OR_NULL(root))
+	if (IS_ERR_OR_NULL(root)) {
+		if (IS_ENABLED(CONFIG_DEBUG_FS) &&
+		    !IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
+			dev_warn(floor->dev.parent,
+				 "CONFIG_MTD_PARTITIONED_MASTER must be enabled to expose debugfs stuff\n");
 		return;
+	}
 
 	debugfs_create_file("docg3_flashcontrol", S_IRUSR, root, docg3,
 			    &flashcontrol_fops);
diff --git a/drivers/mtd/nand/nandsim.c b/drivers/mtd/nand/nandsim.c
index 246b4393118e..44322a363ba5 100644
--- a/drivers/mtd/nand/nandsim.c
+++ b/drivers/mtd/nand/nandsim.c
@@ -520,11 +520,16 @@ static int nandsim_debugfs_create(struct nandsim *dev)
 	struct dentry *root = nsmtd->dbg.dfs_dir;
 	struct dentry *dent;
 
-	if (!IS_ENABLED(CONFIG_DEBUG_FS))
+	/*
+	 * Just skip debugfs initialization when the debugfs directory is
+	 * missing.
+	 */
+	if (IS_ERR_OR_NULL(root)) {
+		if (IS_ENABLED(CONFIG_DEBUG_FS) &&
+		    !IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
+			NS_WARN("CONFIG_MTD_PARTITIONED_MASTER must be enabled to expose debugfs stuff\n");
 		return 0;
-
-	if (IS_ERR_OR_NULL(root))
-		return -1;
+	}
 
 	dent = debugfs_create_file("nandsim_wear_report", S_IRUSR,
 				   root, dev, &dfs_fops);
-- 
2.11.0