linux-kernel - Re: [PATCH 3/3] mtd: mtdconcat: add suspend lock handling

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Date:   Mon, 11 Oct 2021 15:27:03 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Sean Nyekjaer <sean@...nix.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.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 3/3] mtd: mtdconcat: add suspend lock handling

On Mon, 11 Oct 2021 15:15:01 +0200
Boris Brezillon <boris.brezillon@...labora.com> wrote:

> On Mon, 11 Oct 2021 13:52:53 +0200
> Sean Nyekjaer <sean@...nix.com> wrote:
> 
> > Use new suspend lock handling for this special case for concatenated
> > MTD devices.
> > 
> > Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking")
> > Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> > ---
> >  drivers/mtd/mtdconcat.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
> > index f685a581df48..c497c851481f 100644
> > --- a/drivers/mtd/mtdconcat.c
> > +++ b/drivers/mtd/mtdconcat.c
> > @@ -561,25 +561,32 @@ static void concat_sync(struct mtd_info *mtd)
> >  
> >  static int concat_suspend(struct mtd_info *mtd)
> >  {
> > +	struct mtd_info *master = mtd_get_master(mtd);
> >  	struct mtd_concat *concat = CONCAT(mtd);
> >  	int i, rc = 0;
> >  
> >  	for (i = 0; i < concat->num_subdev; i++) {
> >  		struct mtd_info *subdev = concat->subdev[i];
> > -		if ((rc = mtd_suspend(subdev)) < 0)
> > +
> > +		down_write(&master->master.suspend_lock);
> > +		if ((rc = __mtd_suspend(subdev)) < 0)
> >  			return rc;
> > +		up_write(&master->master.suspend_lock);
> >  	}
> >  	return rc;
> >  }
> >  
> >  static void concat_resume(struct mtd_info *mtd)
> >  {
> > +	struct mtd_info *master = mtd_get_master(mtd);
> >  	struct mtd_concat *concat = CONCAT(mtd);
> >  	int i;
> >  
> >  	for (i = 0; i < concat->num_subdev; i++) {
> >  		struct mtd_info *subdev = concat->subdev[i];
> > -		mtd_resume(subdev);
> > +		down_write(&master->master.suspend_lock);
> > +		__mtd_resume(subdev);
> > +		up_write(&master->master.suspend_lock);
> >  	}
> >  }
> >    
> 
> Why do we need to implement the _suspend/_resume() hooks here? The
> underlying MTD devices should be suspended at some point (when the
> class ->suspend() method is called on those device), and there's
> nothing mtdconcat-specific to do here. Looks like implementing this
> suspend-all-subdevs loop results in calling mtd->_suspend()/_resume()
> twice, which is useless. The only issue I see is if the subdevices
> haven't been registered to the device model, but that happens, I
> believe we have bigger issues (those devices won't be suspended when
> mtdconcat is not used).


Uh, just had a look at mtd_concat_create() callers, and they indeed
don't register the subdevices, so I guess the suspend-all-subdevs loop
is needed. I really thought mtdconcat was something more generic
aggregating already registered devices...