kernel: support FIT partition parser on mtdblock devices

Allow using the FIT block-device partition partition parser to work on
top of mtdblock devices.
This is more tricky than it sounds as it requires to reorganize the
procedure of registering mtdblock devices in order to avoid locking
troubles caused by the block partition parsers then trying to open
the mtdblock device for reading while locks are still being held.
Fix that by moving the adding of the disks after the entire device
has been probed when locks no longer need to be held.
Also address issue with mtdsuper surfaced when using sub-partitions
which prevented mounting JFFS2 using the /dev/mtdblock* device.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

1 files changed, 103 insertions, 0 deletions

diff --git a/target/linux/generic/hack-5.10/402-mtd-blktrans-call-add-disks-after-mtd-device.patch b/target/linux/generic/hack-5.10/402-mtd-blktrans-call-add-disks-after-mtd-device.patch
new file mode 100644
index 0000000000..bc9e84cac1
--- /dev/null
+++ b/target/linux/generic/hack-5.10/402-mtd-blktrans-call-add-disks-after-mtd-device.patch
@@ -0,0 +1,103 @@
+From 0bccc3722bdd88e8ae995e77ef9f7b77ee4cbdee Mon Sep 17 00:00:00 2001
+From: Daniel Golle <daniel@makrotopia.org>
+Date: Wed, 7 Apr 2021 22:45:54 +0100
+Subject: [PATCH 2/2] mtd: blktrans: call add disks after mtd device
+To: linux-mtd@lists.infradead.org
+Cc: Vignesh Raghavendra <vigneshr@ti.com>,
+    Richard Weinberger <richard@nod.at>,
+    Miquel Raynal <miquel.raynal@bootlin.com>,
+    David Woodhouse <dwmw2@infradead.org>
+
+Calling device_add_disk while holding mtd_table_mutex leads
+to deadlock in case part_bits!=0 as block partition parsers
+will try to open the newly created disks, trying to acquire
+mutex once again.
+Move device_add_disk to additional function called after
+add partitions of an MTD device have been added and locks
+have been released.
+
+Signed-off-by: Daniel Golle <daniel@makrotopia.org>
+---
+ drivers/mtd/mtd_blkdevs.c    | 33 ++++++++++++++++++++++++++-------
+ drivers/mtd/mtdcore.c        |  3 +++
+ include/linux/mtd/blktrans.h |  1 +
+ 3 files changed, 30 insertions(+), 7 deletions(-)
+
+--- a/drivers/mtd/mtd_blkdevs.c
++++ b/drivers/mtd/mtd_blkdevs.c
+@@ -457,13 +457,6 @@ int add_mtd_blktrans_dev(struct mtd_blkt
+ 	if (new->readonly)
+ 		set_disk_ro(gd, 1);
+ 
+-	device_add_disk(&new->mtd->dev, gd, NULL);
+-
+-	if (new->disk_attributes) {
+-		ret = sysfs_create_group(&disk_to_dev(gd)->kobj,
+-					new->disk_attributes);
+-		WARN_ON(ret);
+-	}
+ 	return 0;
+ error4:
+ 	kfree(new->tag_set);
+@@ -475,6 +468,32 @@ error1:
+ 	return ret;
+ }
+ 
++void register_mtd_blktrans_devs(struct mtd_info *mtd)
++{
++	struct mtd_blktrans_ops *tr;
++	struct mtd_blktrans_dev *dev, *next;
++	struct mtd_info *top_mtd;
++	int ret;
++
++	list_for_each_entry(tr, &blktrans_majors, list) {
++		list_for_each_entry_safe(dev, next, &tr->devs, list) {
++			top_mtd = dev->mtd;
++			while (top_mtd->parent)
++				top_mtd = top_mtd->parent;
++
++			if (mtd->index != top_mtd->index)
++				continue;
++
++			device_add_disk(&dev->mtd->dev, dev->disk, NULL);
++			if (dev->disk_attributes) {
++				ret = sysfs_create_group(&disk_to_dev(dev->disk)->kobj,
++							dev->disk_attributes);
++				WARN_ON(ret);
++			}
++		}
++	}
++}
++
+ int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
+ {
+ 	unsigned long flags;
+--- a/drivers/mtd/mtdcore.c
++++ b/drivers/mtd/mtdcore.c
+@@ -32,6 +32,7 @@
+ 
+ #include <linux/mtd/mtd.h>
+ #include <linux/mtd/partitions.h>
++#include <linux/mtd/blktrans.h>
+ 
+ #include "mtdcore.h"
+ 
+@@ -858,6 +859,8 @@ int mtd_device_parse_register(struct mtd
+ 		register_reboot_notifier(&mtd->reboot_notifier);
+ 	}
+ 
++	register_mtd_blktrans_devs(mtd);
++
+ out:
+ 	if (ret && device_is_registered(&mtd->dev))
+ 		del_mtd_device(mtd);
+--- a/include/linux/mtd/blktrans.h
++++ b/include/linux/mtd/blktrans.h
+@@ -76,6 +76,7 @@ extern int deregister_mtd_blktrans(struc
+ extern int add_mtd_blktrans_dev(struct mtd_blktrans_dev *dev);
+ extern int del_mtd_blktrans_dev(struct mtd_blktrans_dev *dev);
+ extern int mtd_blktrans_cease_background(struct mtd_blktrans_dev *dev);
++extern void register_mtd_blktrans_devs(struct mtd_info *mtd);
+ 
+ 
+ #endif /* __MTD_TRANS_H__ */