linux-kernel - Re: [PATCH 3/4] mtd: mchp23k256: add partitioning support

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Date:   Thu, 1 Jun 2017 11:43:40 -0700
From:   Brian Norris <computersforpeace@...il.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Chris Packham <chris.packham@...iedtelesis.co.nz>,
        dwmw2@...radead.org, andrew@...n.ch, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>
Subject: Re: [PATCH 3/4] mtd: mchp23k256: add partitioning support

On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote:
> Hi Chris,
> 
> On Wed, 17 May 2017 17:39:07 +1200
> Chris Packham <chris.packham@...iedtelesis.co.nz> wrote:
> 
> > Setting the of_node for the mtd device allows the generic mtd code to
> > setup the partitions. Additionally we must specify a non-zero erasesize
> > for the partitions to be writeable.
> > 
> > Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> > ---
> >  drivers/mtd/devices/mchp23k256.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/mtd/devices/mchp23k256.c b/drivers/mtd/devices/mchp23k256.c
> > index 2542f5b8b63f..02c6b9dcbd3e 100644
> > --- a/drivers/mtd/devices/mchp23k256.c
> > +++ b/drivers/mtd/devices/mchp23k256.c
> > @@ -143,6 +143,7 @@ static int mchp23k256_probe(struct spi_device *spi)
> >  
> >  	data = dev_get_platdata(&spi->dev);
> >  
> > +	mtd_set_of_node(&flash->mtd, spi->dev.of_node);
> >  	flash->mtd.dev.parent	= &spi->dev;
> >  	flash->mtd.type		= MTD_RAM;
> >  	flash->mtd.flags	= MTD_CAP_RAM;
> > @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi)
> >  	flash->mtd._read	= mchp23k256_read;
> >  	flash->mtd._write	= mchp23k256_write;
> >  
> > +	flash->mtd.erasesize = PAGE_SIZE;
> > +	while (flash->mtd.size & (flash->mtd.erasesize - 1))
> > +		flash->mtd.erasesize >>= 1;
> > +
> 
> Can we fix allocate_partition() to properly handle the
> master->erasesize == 0 case instead of doing that?

Is everything actually ready for the eraseblock size to be 0? That would
seem surprising to many applications, I would think. Can you, for
instance, even use UBI on such a device?

BTW, I feel like this check is a little more natural to do with
'mtd->flags & MTD_NO_ERASE', rather than checking the (apparently
meaningless) erasesize.

(I realize there's a later version of these patches, but I figured I'd
put my comments where the suggestion was brought up.)

Brian