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

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Message-ID: <20211213101025.42c27b43@xps13>
Date:   Mon, 13 Dec 2021 10:10:25 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Sean Nyekjaer <sean@...nix.com>
Cc:     Boris Brezillon <boris.brezillon@...labora.com>,
        linux-kernel@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        linux-mtd@...ts.infradead.org
Subject: Re: [PATCH v5 3/4] mtd: core: protect access to MTD devices while
 in suspend

Hi Sean,

sean@...nix.com wrote on Fri, 10 Dec 2021 14:25:35 +0100:

> On Thu, Dec 09, 2021 at 03:28:11PM +0100, Miquel Raynal wrote:
> > Hi Sean,
> > 
> > sean@...nix.com 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?

I haven't thought about it extensively, an atomic variable sound fine
but I am definitely not a locking expert...

> 
> /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;


Thanks,
Miquèl