linux-kernel - Re: [PATCH 0/3] mtd: core: protect access to mtd devices while in suspend

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Message-ID: <20211019180800.3v7emokse6lkpjvk@skn-laptop>
Date:   Tue, 19 Oct 2021 20:08:00 +0200
From:   Sean Nyekjaer <sean@...nix.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Boris Brezillon <boris.brezillon@...labora.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] mtd: core: protect access to mtd devices while in
 suspend

On Fri, Oct 15, 2021 at 08:22:06AM +0200, Miquel Raynal wrote:
> Hi Sean,
> 
> boris.brezillon@...labora.com wrote on Mon, 11 Oct 2021 16:05:46 +0200:
> 
> > On Mon, 11 Oct 2021 13:52:50 +0200

[ ... ]

> 
> > > One (small) issue still present. gpmi_nand.c uses the rwsem before it's
> > > initialized. Seems cumbersome to have every mtd/nand driver to call
> > > init_waitqueue_head() and init_rwsem(). Could we somehow move the call
> > > to mtd_set_dev_defaults() before nand_create_bbt()?  
> > 
> > I have a nasty trick for that one, but I'm not sure Miquel will like it
> > (actually, I don't like it either, but it's so simple compared to the
> > other options we have that I'm tempted to go for this approach until
> > someone has time to invest in a cleaner solution :-)):
> > 
> > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > index 3d6c6e880520..a9ac2d528a4d 100644
> > --- a/drivers/mtd/nand/raw/nand_base.c
> > +++ b/drivers/mtd/nand/raw/nand_base.c
> > @@ -6222,8 +6222,6 @@ static int nand_scan_tail(struct nand_chip *chip)
> >         mtd->_sync = nand_sync;
> >         mtd->_lock = nand_lock;
> >         mtd->_unlock = nand_unlock;
> > -       mtd->_suspend = nand_suspend;
> > -       mtd->_resume = nand_resume;
> >         mtd->_reboot = nand_shutdown;
> >         mtd->_block_isreserved = nand_block_isreserved;
> >         mtd->_block_isbad = nand_block_isbad;
> > @@ -6269,6 +6267,13 @@ static int nand_scan_tail(struct nand_chip *chip)
> >         if (ret)
> >                 goto err_free_secure_regions;
> >  
> > +       /*
> > +        * Populate the suspend/resume hooks after the BBT has been scanned to
> > +        * avoid using the suspend lock and resume waitqueue which are only
> > +        * initialized when mtd_device_register() is called.
> > +        */
> > +       mtd->_suspend = nand_suspend;
> > +       mtd->_resume = nand_resume;
> >         return 0;
> 
> I'm fine with this as long as it is documented for now.
> 

Hi Boris and Miquel,

gpmi-nand.c sets NAND_SKIP_BBTSCAN so we won't get there and populate
suspend resume hooks :(
Guess there is other drivers that does the same thing...

I have looked in the history and tried to blame gpmi-nand.c, but I can't
see the reason to why NAND_SKIP_BBTSCAN is set.

I have tested Boris' hack with this diff (and it seems to work):

diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
index 4d08e4ab5c1b..ec7f44d630b6 100644
--- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
+++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
@@ -2073,8 +2073,6 @@ static int gpmi_nand_attach_chip(struct nand_chip *chip)
 	if (ret)
 		return ret;
 
-	chip->options |= NAND_SKIP_BBTSCAN;
-
 	return 0;
 }
 
@@ -2460,9 +2459,6 @@ static int gpmi_nand_init(struct gpmi_nand_data *this)
 		goto err_out;
 
 	ret = nand_boot_init(this);
-	if (ret)
-		goto err_nand_cleanup;
-	ret = nand_create_bbt(chip);
 	if (ret)
 		goto err_nand_cleanup;
 

Do I miss something?

/Sean