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

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Message-ID: <20211011133556.probhbuowxkumpzb@skn-laptop>
Date:   Mon, 11 Oct 2021 15:35:56 +0200
From:   Sean Nyekjaer <sean@...nix.com>
To:     Boris Brezillon <boris.brezillon@...labora.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, Oct 11, 2021 at 03:27:03PM +0200, Boris Brezillon wrote:
> 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...

Hi Boris,

Cool, mtd_concat should be seen as mtd devices concatenated? Could be
spi-nors and rawnand. So _suspend() needs to be called for every device
layer?

>From what I see here, mtd_suspend()/mtd_resume() is called for every mtd
device. Before this patch mtd_suspend() would only have effect on the
first device as master->master.suspended is set and then calls to
device specific _suspend() is skipped.

Correct?

/Sean