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Date:   Wed, 20 Oct 2021 09:12:28 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Boris Brezillon <boris.brezillon@collabora.com>
Cc:     Sean Nyekjaer <sean@geanix.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Boris Brezillon <bbrezillon@kernel.org>,
        linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] mtd: core: protect access to mtd devices while in
 suspend
Message-ID: <20211020091228.136fde6e@xps13>
In-Reply-To: <20211020090058.58af1087@collabora.com>
References: <20211011115253.38497-1-sean@geanix.com>
        <20211011160546.707b737b@collabora.com>
        <20211015082206.244a2316@xps13>
        <20211019180800.3v7emokse6lkpjvk@skn-laptop>
        <20211020085250.030ef244@collabora.com>
        <20211020090058.58af1087@collabora.com>
Organization: Bootlin
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Hi Boris,

boris.brezillon@collabora.com wrote on Wed, 20 Oct 2021 09:00:58 +0200:

> On Wed, 20 Oct 2021 08:52:50 +0200
> Boris Brezillon <boris.brezillon@collabora.com> wrote:
> 
> > On Tue, 19 Oct 2021 20:08:00 +0200
> > Sean Nyekjaer <sean@geanix.com> wrote:
> >   
> > > On Fri, Oct 15, 2021 at 08:22:06AM +0200, Miquel Raynal wrote:    
> > > > Hi Sean,
> > > > 
> > > > boris.brezillon@collabora.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...    
> > 
> > This should fix the issue:
> > 
> > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > index 3d6c6e880520..c92b17f66994 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;
> > @@ -6262,13 +6260,21 @@ static int nand_scan_tail(struct nand_chip *chip)
> >  
> >         /* Check, if we should skip the bad block table scan */
> >         if (chip->options & NAND_SKIP_BBTSCAN)
> > -               return 0;
> > +               goto out;
> >  
> >         /* Build bad block table */
> >         ret = nand_create_bbt(chip);
> >         if (ret)
> >                 goto err_free_secure_regions;
> >  
> > +out:
> > +       /*
> > +        * 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;
> >  
> >  err_free_secure_regions:  
> 
> Actually, this version is even cleaner:
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index 3d6c6e880520..98c39b7f6279 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;
> @@ -6261,14 +6259,20 @@ static int nand_scan_tail(struct nand_chip *chip)
>                 goto err_free_interface_config;
>  
>         /* Check, if we should skip the bad block table scan */
> -       if (chip->options & NAND_SKIP_BBTSCAN)
> -               return 0;
> -
> -       /* Build bad block table */
> -       ret = nand_create_bbt(chip);
> -       if (ret)
> -               goto err_free_secure_regions;
> +       if (chip->options & NAND_SKIP_BBTSCAN) {
> +               /* Build bad block table */
> +               ret = nand_create_bbt(chip);
> +               if (ret)
> +                       goto err_free_secure_regions;
> +       }

Nice idea.

>  
> +       /*
> +        * 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;
>  
>  err_free_secure_regions:

Cheers,
Miquèl