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

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Message-ID: <bba73e6d5f4b41a88423287300d892e5@svr-chch-ex1.atlnz.lc>
Date:   Thu, 1 Jun 2017 21:30:07 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>
CC:     "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.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 02/06/17 06:43, Brian Norris wrote:
> 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 was my initial motivation for faking it.

> That would
> seem surprising to many applications, I would think. Can you, for
> instance, even use UBI on such a device?

I've tried ext2 and I believe Andrew has tried minix fs. We're talking 
SRAM so UBI/UBIFS doesn't really provide much benefit for this use-case.

> 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
>