linux-kernel - Re: [RFC PATCH 0/7] mtd: partitions: add of_match

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Date:	Fri, 11 Dec 2015 09:44:37 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	MTD Maling List <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Simon Arlott <simon@...e.lp0.eu>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Jonas Gorski <jogo@...nwrt.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	devicetree-spec@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Rafał Miłecki <zajec5@...il.com>,
	Hauke Mehrtens <hauke@...ke-m.de>,
	Arnd Bergmann <arnd@...db.de>,
	David Hendricks <dhendrix@...omium.org>
Subject: Re: [RFC PATCH 0/7] mtd: partitions: add of_match_table support

Hi Brian,

On Thu, Dec 10, 2015 at 9:54 PM, Brian Norris
<computersforpeace@...il.com> wrote:
> On Sat, Dec 05, 2015 at 11:15:54AM +0100, Geert Uytterhoeven wrote:
>> On Sat, Dec 5, 2015 at 6:19 AM, Brian Norris
>> <computersforpeace@...il.com> wrote:
>> > There have been several discussions [1] about adding a device tree binding for
>> > associating flash devices with the partition parser(s) that are used on the
>> > flash. There are a few reasons:
>> >
>> >  (1) drivers shouldn't have to be encoding platform knowledge by listing what
>> >      parsers might be used on a given system (this is the currently all that's
>> >      supported)
>> >  (2) we can't just scan for all supported parsers (like the block system does), since
>> >      there is a wide diversity of "formats" (no standardization), and it is not
>> >      always safe or efficient to attempt to do so, particularly since many of
>> >      them allow their data structures to be placed anywhere on the flash, and
>> >      so require scanning the entire flash device to find them.
>>
>> I read the second reason, but would it be useful to (partially) merge
>> block/partitions/ and drivers/mtd/partitions/, so I can use e.g. msdos
>> partitions
>> on an mtd device??
>
> I kinda agree with Michal: is there a good use case?

I don't have an immediate use case.
Just looking at it from a high-level viewpoint.

> Really, MTD partitioning is not a highly-scalable design. Particularly,
> it's not typically that well-suited to large (read: unreliable) NAND
> flash, where fixing partitions at the raw flash level mostly serves to
> restrict UBI's ability to wear-level across the device. For that sort of
> case, it's best if people are using UBI volumes on a (mostly?)
> unpartitioned MTD, instead of using MTD partitions as the main
> separation mechanism. Also, most partition designs (either MTD or block)
> aren't very robust against bitflips, read disturb, etc.
>
> IOW, I wouldn't expect MBR or GPT to work well on large raw NAND flash,
> and so I don't plan to do that sort of work myself. If you can provide
> some better argument for it, and some nice maintainable code to go with
> it, then of course it could be considered :)

There's also NOR FLASH (e.g. SPI-NOR), which is what most boards I'm
working on have.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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