mtd: mtdcore: add debugfs nodes for querying the flash name and id

Currently, we don't have vfs nodes for querying the underlying flash name
and flash id. This information is important especially when we want to
know the flash detail of the defective system. In order to support the
query, we add mtd_debugfs_populate() to create two debugfs nodes
(ie. partname and partid). The upper driver can assign the pointer to
partname and partid before calling mtd_device_register().

Signed-off-by: Zhuohao Lee <[e-mail]>
Reviewed-by: Boris Brezillon <[e-mail]>
Signed-off-by: Tudor Ambarus <[e-mail]>

drivers/mtd/mtdcore.c

···
 	.release	= mtd_release,
 };
 
+static int mtd_partid_show(struct seq_file *s, void *p)
+{
+	struct mtd_info *mtd = s->private;
+
+	seq_printf(s, "%s\n", mtd->dbg.partid);
+
+	return 0;
+}
+
+static int mtd_partid_debugfs_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, mtd_partid_show, inode->i_private);
+}
+
+static const struct file_operations mtd_partid_debug_fops = {
+	.open           = mtd_partid_debugfs_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+
+static int mtd_partname_show(struct seq_file *s, void *p)
+{
+	struct mtd_info *mtd = s->private;
+
+	seq_printf(s, "%s\n", mtd->dbg.partname);
+
+	return 0;
+}
+
+static int mtd_partname_debugfs_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, mtd_partname_show, inode->i_private);
+}
+
+static const struct file_operations mtd_partname_debug_fops = {
+	.open           = mtd_partname_debugfs_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+
+static struct dentry *dfs_dir_mtd;
+
+static void mtd_debugfs_populate(struct mtd_info *mtd)
+{
+	struct device *dev = &mtd->dev;
+	struct dentry *root, *dent;
+
+	if (IS_ERR_OR_NULL(dfs_dir_mtd))
+		return;
+
+	root = debugfs_create_dir(dev_name(dev), dfs_dir_mtd);
+	if (IS_ERR_OR_NULL(root)) {
+		dev_dbg(dev, "won't show data in debugfs\n");
+		return;
+	}
+
+	mtd->dbg.dfs_dir = root;
+
+	if (mtd->dbg.partid) {
+		dent = debugfs_create_file("partid", 0400, root, mtd,
+					   &mtd_partid_debug_fops);
+		if (IS_ERR_OR_NULL(dent))
+			dev_err(dev, "can't create debugfs entry for partid\n");
+	}
+
+	if (mtd->dbg.partname) {
+		dent = debugfs_create_file("partname", 0400, root, mtd,
+					   &mtd_partname_debug_fops);
+		if (IS_ERR_OR_NULL(dent))
+			dev_err(dev,
+				"can't create debugfs entry for partname\n");
+	}
+}
+
 #ifndef CONFIG_MMU
 unsigned mtd_mmap_capabilities(struct mtd_info *mtd)
 {
···
 	return 0;
 }
 
-static struct dentry *dfs_dir_mtd;
-
 /**
  *	add_mtd_device - register an MTD device
  *	@mtd: pointer to new MTD device info structure
···
 	if (error)
 		goto fail_nvmem_add;
 
-	if (!IS_ERR_OR_NULL(dfs_dir_mtd)) {
-		mtd->dbg.dfs_dir = debugfs_create_dir(dev_name(&mtd->dev), dfs_dir_mtd);
-		if (IS_ERR_OR_NULL(mtd->dbg.dfs_dir)) {
-			pr_debug("mtd device %s won't show data in debugfs\n",
-				 dev_name(&mtd->dev));
-		}
-	}
+	mtd_debugfs_populate(mtd);
 
 	device_create(&mtd_class, mtd->dev.parent, MTD_DEVT(i) + 1, NULL,
 		      "mtd%dro", i);

include/linux/mtd/mtd.h

···
  */
 struct mtd_debug_info {
 	struct dentry *dfs_dir;
+
+	const char *partname;
+	const char *partid;
 };
 
 struct mtd_info {