Re: [PATCH v5 3/4] mtd: core: protect access to MTD devices while in suspend

[Sean Nyekjaer]

On Thu, Dec 09, 2021 at 03:28:11PM +0100, Miquel Raynal wrote:
> Hi Sean,
> 
> sean@xxxxxxxxxx wrote on Thu, 9 Dec 2021 15:07:21 +0100:
> 
> > On Fri, Dec 03, 2021 at 02:39:58PM +0100, Miquel Raynal wrote:
> > > Hello,
> > >   
> > > > > Fine by me, lets drop this series.  
> > > 
> > > FYI I've dropped the entire series from mtd/next. I'm waiting for the
> > > fix discussed below (without abusing the chip mutex ;-) ).  
> > 
> > Cool, looking forward to test a patch series :)
> 
> Test? You mean "write"? :)
> 
> Cheers,
> Miquèl

Hi Miquel,

Should we us a atomic for the suspended variable?

/Sean

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index b3a9bc08b4bb..eb4ec9a42d49 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -338,16 +338,19 @@ static int nand_isbad_bbm(struct nand_chip *chip, loff_t ofs)
  *
  * Return: -EBUSY if the chip has been suspended, 0 otherwise
  */
-static int nand_get_device(struct nand_chip *chip)
+static void nand_get_device(struct nand_chip *chip)
 {
-	mutex_lock(&chip->lock);
-	if (chip->suspended) {
+	/* Wait until the device is resumed. */
+	while (1) {
+		mutex_lock(&chip->lock);
+		if (!chip->suspended) {
+			mutex_lock(&chip->controller->lock);
+			return;
+		}
 		mutex_unlock(&chip->lock);
-		return -EBUSY;
-	}
-	mutex_lock(&chip->controller->lock);
 
-	return 0;
+		wait_event(chip->resume_wq, !chip->suspended);
+	}
 }
 
 /**
@@ -576,9 +579,7 @@ static int nand_block_markbad_lowlevel(struct nand_chip *chip, loff_t ofs)
 		nand_erase_nand(chip, &einfo, 0);
 
 		/* Write bad block marker to OOB */
-		ret = nand_get_device(chip);
-		if (ret)
-			return ret;
+		nand_get_device(chip);
 
 		ret = nand_markbad_bbm(chip, ofs);
 		nand_release_device(chip);
@@ -3759,9 +3760,7 @@ static int nand_read_oob(struct mtd_info *mtd, loff_t from,
 	    ops->mode != MTD_OPS_RAW)
 		return -ENOTSUPP;
 
-	ret = nand_get_device(chip);
-	if (ret)
-		return ret;
+	nand_get_device(chip);
 
 	if (!ops->datbuf)
 		ret = nand_do_read_oob(chip, from, ops);
@@ -4352,9 +4351,7 @@ static int nand_write_oob(struct mtd_info *mtd, loff_t to,
 
 	ops->retlen = 0;
 
-	ret = nand_get_device(chip);
-	if (ret)
-		return ret;
+	nand_get_device(chip);
 
 	switch (ops->mode) {
 	case MTD_OPS_PLACE_OOB:
@@ -4414,9 +4411,7 @@ int nand_erase_nand(struct nand_chip *chip, struct erase_info *instr,
 		return -EIO;
 
 	/* Grab the lock and see if the device is available */
-	ret = nand_get_device(chip);
-	if (ret)
-		return ret;
+	nand_get_device(chip);
 
 	/* Shift to get first page */
 	page = (int)(instr->addr >> chip->page_shift);
@@ -4503,7 +4498,7 @@ static void nand_sync(struct mtd_info *mtd)
 	pr_debug("%s: called\n", __func__);
 
 	/* Grab the lock and see if the device is available */
-	WARN_ON(nand_get_device(chip));
+	nand_get_device(chip);
 	/* Release it and go back */
 	nand_release_device(chip);
 }
@@ -4520,9 +4515,7 @@ static int nand_block_isbad(struct mtd_info *mtd, loff_t offs)
 	int ret;
 
 	/* Select the NAND device */
-	ret = nand_get_device(chip);
-	if (ret)
-		return ret;
+	nand_get_device(chip);
 
 	nand_select_target(chip, chipnr);
 
@@ -4593,6 +4586,8 @@ static void nand_resume(struct mtd_info *mtd)
 			__func__);
 	}
 	mutex_unlock(&chip->lock);
+
+	wake_up_all(&chip->resume_wq);
 }
 
 /**
@@ -5370,6 +5365,7 @@ static int nand_scan_ident(struct nand_chip *chip, unsigned int maxchips,
 	chip->cur_cs = -1;
 
 	mutex_init(&chip->lock);
+	init_waitqueue_head(&chip->resume_wq);
 
 	/* Enforce the right timings for reset/detection */
 	chip->current_interface_config = nand_get_reset_interface_config();
diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
index b2f9dd3cbd69..248054560581 100644
--- a/include/linux/mtd/rawnand.h
+++ b/include/linux/mtd/rawnand.h
@@ -1294,6 +1294,7 @@ struct nand_chip {
 	/* Internals */
 	struct mutex lock;
 	unsigned int suspended : 1;
+	wait_queue_head_t resume_wq;
 	int cur_cs;
 	int read_retries;
 	struct nand_secure_region *secure_regions;