mtd: rawnand: Simplify the locking

nand_get_device() was complex for apparently no good reason. Let's
replace this locking scheme with 2 mutexes: one attached to the
controller and another one attached to the chip.

Every time the core calls nand_get_device(), it will first lock the
chip and if the chip is not suspended, will then lock the controller.
nand_release_device() will release both lock in the reverse order.

nand_get_device() can sleep, just like the previous implementation,
which means you should never call that from an atomic context.

We also get rid of

- the chip->state field, since all it was used for was flagging the
  chip as suspended. We replace it by a field called chip->suspended
  and directly set it from nand_suspend/resume()
- the controller->wq and controller->active fields which are no longer
  needed since the new controller->lock (now a mutex) guarantees that
  all operations are serialized at the controller level
- panic_nand_get_device() which would anyway be a no-op. Talking about
  panic write, I keep thinking the rawnand implementation is unsafe
  because there's not negotiation with the controller to know when it's
  actually done with it's previous operation. I don't intend to fix
  that here, but that's probably something we should look at, or maybe
  we should consider dropping the ->_panic_write() implementation

Last important change to mention: we now return -EBUSY when someone
tries to access a device that as been suspended, and propagate this
error to the upper layer.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

1 files changed, 9 insertions, 15 deletions

diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
index 33e240acdc6d..17d2d9ae33bf 100644
--- a/include/linux/mtd/rawnand.h
+++ b/include/linux/mtd/rawnand.h
@@ -16,13 +16,12 @@
 #ifndef __LINUX_MTD_RAWNAND_H
 #define __LINUX_MTD_RAWNAND_H
 
-#include <linux/wait.h>
-#include <linux/spinlock.h>
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/flashchip.h>
 #include <linux/mtd/bbm.h>
 #include <linux/mtd/jedec.h>
 #include <linux/mtd/onfi.h>
+#include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/types.h>
 
@@ -897,25 +896,17 @@ struct nand_controller_ops {
 /**
  * struct nand_controller - Structure used to describe a NAND controller
  *
- * @lock:               protection lock
- * @active:		the mtd device which holds the controller currently
- * @wq:			wait queue to sleep on if a NAND operation is in
- *			progress used instead of the per chip wait queue
- *			when a hw controller is available.
+ * @lock:		lock used to serialize accesses to the NAND controller
  * @ops:		NAND controller operations.
  */
 struct nand_controller {
-	spinlock_t lock;
-	struct nand_chip *active;
-	wait_queue_head_t wq;
+	struct mutex lock;
 	const struct nand_controller_ops *ops;
 };
 
 static inline void nand_controller_init(struct nand_controller *nfc)
 {
-	nfc->active = NULL;
-	spin_lock_init(&nfc->lock);
-	init_waitqueue_head(&nfc->wq);
+	mutex_init(&nfc->lock);
 }
 
 /**
@@ -983,7 +974,6 @@ struct nand_legacy {
  *			setting the read-retry mode. Mostly needed for MLC NAND.
  * @ecc:		[BOARDSPECIFIC] ECC control structure
  * @buf_align:		minimum buffer alignment required by a platform
- * @state:		[INTERN] the current state of the NAND device
  * @oob_poi:		"poison value buffer," used for laying out OOB data
  *			before writing
  * @page_shift:		[INTERN] number of address bits in a page (column
@@ -1034,6 +1024,9 @@ struct nand_legacy {
  *			cur_cs < numchips. NAND Controller drivers should not
  *			modify this value, but they're allowed to read it.
  * @read_retries:	[INTERN] the number of read retry modes supported
+ * @lock:		lock protecting the suspended field. Also used to
+ *			serialize accesses to the NAND device.
+ * @suspended:		set to 1 when the device is suspended, 0 when it's not.
  * @bbt:		[INTERN] bad block table pointer
  * @bbt_td:		[REPLACEABLE] bad block table descriptor for flash
  *			lookup.
@@ -1088,7 +1081,8 @@ struct nand_chip {
 
 	int read_retries;
 
-	flstate_t state;
+	struct mutex lock;
+	unsigned int suspended : 1;
 
 	uint8_t *oob_poi;
 	struct nand_controller *controller;