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

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Date:   Thu, 1 Jun 2017 23:08:08 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Brian Norris <computersforpeace@...il.com>
CC:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        "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 10:23, Brian Norris wrote:
> On Thu, Jun 01, 2017 at 09:30:07PM +0000, Chris Packham wrote:
>> On 02/06/17 06:43, Brian Norris wrote:
>>> On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote:
>>>> 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.
> 
> Understood. I think it's probably better to avoid hacking drivers like
> you were about to, but I was also curious if anyone had thought through
> the implications of *not* forcing a non-zero size.
> 
>>> 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.
> 
> Right. But that's not necessarily true for all NO_ERASE devices, so we'd
> probably want to think about that before allowing it.

Do we need a flag to indicate SRAM-like properties? I assume there is a 
difference between NO_ERASE on ROM devices where there is just no way of 
erasing the data. For {S,F,M}RAM there is no block erase operation but 
you can overwrite data to destroy it (which is actually my use-case with 
this SPI SRAM). I was tempted to set erase_size = 1 at one point which 
in my mind was technically accurate but would probably upset the mtd 
layer just as much as 0.