[PATCH v2] mtd: core: expose ooblayout information via debugfs

[Gabor Juhos <j4g8y7@gmail.com>]

Add two new debugfs files which allows to determine the OOB layout
used by a given MTD device. This can be useful to verify the current
layout during driver development without adding extra debug code.
The exposed information also makes it easier to analyze NAND dumps
without the need of crawling out the layout from the driver code.

The content of the new debugfs files is similar to this:

    # cat /sys/kernel/debug/mtd/mtd0/ooblayout_ecc
    0      0   49
    1     65   63
    # cat /sys/kernel/debug/mtd/mtd0/ooblayout_free
    0     49   16

Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
---
Changes in v2:
  - rebase on tip of mtd/next
  - expose informations via debugfs instead of sysfs
  - drop sysfs ABI documentation changes
  - update subject and commit description
  - Link to v1: https://lore.kernel.org/r/20250719-mtd-ooblayout-sysfs-v1-1-e0d68d872e17@gmail.com
---
 drivers/mtd/mtdcore.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 5ba9a741f5ac3c297ae21329c2827baf5dc471f0..6a1a514021730fb4baafbf3803e900a9ed6b21b2 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -384,14 +384,64 @@ EXPORT_SYMBOL_GPL(mtd_check_expert_analysis_mode);
 
 static struct dentry *dfs_dir_mtd;
 
+static int mtd_ooblayout_show(struct seq_file *s, void *p,
+			      int (*iter)(struct mtd_info *, int section,
+			      struct mtd_oob_region *region))
+{
+	struct mtd_info *mtd = s->private;
+	int section;
+
+	for (section = 0;; section++) {
+		struct mtd_oob_region region;
+		int err;
+
+		err = iter(mtd, section, &region);
+		if (err) {
+			if (err == -ERANGE)
+				break;
+
+			return err;
+		}
+
+		seq_printf(s, "%-3d %4u %4u\n", section, region.offset,
+			   region.length);
+	}
+
+	return 0;
+}
+
+static int mtd_ooblayout_ecc_show(struct seq_file *s, void *p)
+{
+	return mtd_ooblayout_show(s, p, mtd_ooblayout_ecc);
+}
+DEFINE_SHOW_ATTRIBUTE(mtd_ooblayout_ecc);
+
+static int mtd_ooblayout_free_show(struct seq_file *s, void *p)
+{
+	return mtd_ooblayout_show(s, p, mtd_ooblayout_free);
+}
+DEFINE_SHOW_ATTRIBUTE(mtd_ooblayout_free);
+
 static void mtd_debugfs_populate(struct mtd_info *mtd)
 {
 	struct device *dev = &mtd->dev;
+	struct mtd_oob_region region;
 
 	if (IS_ERR_OR_NULL(dfs_dir_mtd))
 		return;
 
 	mtd->dbg.dfs_dir = debugfs_create_dir(dev_name(dev), dfs_dir_mtd);
+	if (IS_ERR_OR_NULL(mtd->dbg.dfs_dir))
+		return;
+
+	/* Create ooblayout files only if at least one region is present. */
+	if (mtd_ooblayout_ecc(mtd, 0, &region) == 0)
+		debugfs_create_file("ooblayout_ecc", 0444, mtd->dbg.dfs_dir,
+				    mtd, &mtd_ooblayout_ecc_fops);
+
+	if (mtd_ooblayout_free(mtd, 0, &region) == 0)
+		debugfs_create_file("ooblayout_free", 0444, mtd->dbg.dfs_dir,
+				    mtd, &mtd_ooblayout_free_fops);
 }
 
 #ifndef CONFIG_MMU

---
base-commit: 9cf9db888f387844e063efc6296e9fa5c042995e
change-id: 20250719-mtd-ooblayout-sysfs-77af651b3738

Best regards,
-- 
Gabor Juhos <j4g8y7@gmail.com>