mtd: implement proper partition handling

Instead of collecting partitions in a flat list, create a hierarchy
within the mtd_info structure: use a partitions list to keep track of
the partitions of an MTD device (which might be itself a partition of
another MTD device), a pointer to the parent device (NULL when the MTD
device is the root one, not a partition).

By also saving directly in mtd_info the offset of the partition, we
can get rid of the mtd_part structure.

While at it, be consistent in the naming of the mtd_info structures to
ease the understanding of the new hierarchy: these structures are
usually called 'mtd', unless there are multiple instances of the same
structure. In this case, there is usually a parent/child bound so we
will call them 'parent' and 'child'.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200114090952.11232-1-miquel.raynal@bootlin.com

drivers/mtd/mtdchar.c

@@ -349,6 +349,7 @@ static int mtdchar_writeoob(struct file *file, struct mtd_info *mtd,
 	uint64_t start, uint32_t length, void __user *ptr,
 	uint32_t __user *retp)
 {
+	struct mtd_info *master  = mtd_get_master(mtd);
 	struct mtd_file_info *mfi = file->private_data;
 	struct mtd_oob_ops ops = {};
 	uint32_t retlen;
@@ -360,7 +361,7 @@ static int mtdchar_writeoob(struct file *file, struct mtd_info *mtd,
 	if (length > 4096)
 		return -EINVAL;
 
-	if (!mtd->_write_oob)
+	if (!master->_write_oob)
 		return -EOPNOTSUPP;
 
 	ops.ooblen = length;
@@ -586,6 +587,7 @@ static int mtdchar_blkpg_ioctl(struct mtd_info *mtd,
 static int mtdchar_write_ioctl(struct mtd_info *mtd,
 		struct mtd_write_req __user *argp)
 {
+	struct mtd_info *master = mtd_get_master(mtd);
 	struct mtd_write_req req;
 	struct mtd_oob_ops ops = {};
 	const void __user *usr_data, *usr_oob;
@@ -597,9 +599,8 @@ static int mtdchar_write_ioctl(struct mtd_info *mtd,
 	usr_data = (const void __user *)(uintptr_t)req.usr_data;
 	usr_oob = (const void __user *)(uintptr_t)req.usr_oob;
 
-	if (!mtd->_write_oob)
+	if (!master->_write_oob)
 		return -EOPNOTSUPP;
-
 	ops.mode = req.mode;
 	ops.len = (size_t)req.len;
 	ops.ooblen = (size_t)req.ooblen;
@@ -635,6 +636,7 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 {
 	struct mtd_file_info *mfi = file->private_data;
 	struct mtd_info *mtd = mfi->mtd;
+	struct mtd_info *master = mtd_get_master(mtd);
 	void __user *argp = (void __user *)arg;
 	int ret = 0;
 	struct mtd_info_user info;
@@ -824,7 +826,7 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 	{
 		struct nand_oobinfo oi;
 
-		if (!mtd->ooblayout)
+		if (!master->ooblayout)
 			return -EOPNOTSUPP;
 
 		ret = get_oobinfo(mtd, &oi);
@@ -918,7 +920,7 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 	{
 		struct nand_ecclayout_user *usrlay;
 
-		if (!mtd->ooblayout)
+		if (!master->ooblayout)
 			return -EOPNOTSUPP;
 
 		usrlay = kmalloc(sizeof(*usrlay), GFP_KERNEL);