linux-kernel - Re: [PATCH 4/9] mtd: devices: add AT24 eeprom support

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Date: Tue, 2 Jul 2024 16:34:24 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Tudor Ambarus <tudor.ambarus@...aro.org>, 
	Marco Felsch <m.felsch@...gutronix.de>, Miquel Raynal <miquel.raynal@...tlin.com>, 
	Richard Weinberger <richard@....at>, Vignesh Raghavendra <vigneshr@...com>, 
	Arnd Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Russell King <linux@...linux.org.uk>, 
	Joel Stanley <joel@....id.au>, Andrew Jeffery <andrew@...econstruct.com.au>, 
	Nicolas Ferre <nicolas.ferre@...rochip.com>, Alexandre Belloni <alexandre.belloni@...tlin.com>, 
	Claudiu Beznea <claudiu.beznea@...on.dev>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, Vladimir Zapolskiy <vz@...ia.com>, Andrew Lunn <andrew@...n.ch>, 
	Gregory Clement <gregory.clement@...tlin.com>, Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>, 
	Tony Lindgren <tony@...mide.com>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Magnus Damm <magnus.damm@...il.com>, Dinh Nguyen <dinguyen@...nel.org>, 
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	Nicholas Piggin <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
	Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, linux-mtd@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-aspeed@...ts.ozlabs.org, imx@...ts.linux.dev, linux-omap@...r.kernel.org, 
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	linuxppc-dev@...ts.ozlabs.org, linux-mips@...r.kernel.org, loongarch@...ts.linux.dev
Subject: Re: [PATCH 4/9] mtd: devices: add AT24 eeprom support

On Tue, Jul 02, 2024 at 04:15:20PM GMT, Pratyush Yadav wrote:
> On Tue, Jul 02 2024, Maxime Ripard wrote:
> 
> > On Tue, Jul 02, 2024 at 03:41:52PM GMT, Pratyush Yadav wrote:
> >> On Mon, Jul 01 2024, Tudor Ambarus wrote:
> >> 
> >> > On 7/1/24 2:53 PM, Marco Felsch wrote:
> >> >> EEPROMs can become quite large nowadays (>=64K). Exposing such devices
> >> >> as single device isn't always sufficient. There may be partitions which
> >> >> require different access permissions. Also write access always need to
> >> >> to verify the offset.
> >> >> 
> >> >> Port the current misc/eeprom/at24.c driver to the MTD framework since
> >> >> EEPROMs are memory-technology devices and the framework already supports
> >> >
> >> > I was under the impression that MTD devices are tightly coupled by erase
> >> > blocks. But then we see MTD_NO_ERASE, so what are MTD devices after all?
> >> 
> >> I was curious as well so I did some digging.
> >> 
> [...]
> >> 
> >> I also found a thread from 2013 by Maxime Ripard (+Cc) suggesting adding
> >> EEPROMs to MTD [1]. The main purpose would have been unifying the EEPROM
> >> drivers under a single interface. I am not sure what came of it though,
> >> since I can't find any patches that followed up with the proposal.
> >
> > That discussion led to drivers/nvmem after I started to work on
> > some early prototype, and Srinivas took over that work.
> 
> So would you say it is better for EEPROM drivers to use nvmem instead of
> moving under MTD?

I thought so at the time, but that was more than 10y ago, and I have
followed neither nvmem nor MTD since so I don't really have an opinion
there.

It looks like drivers/misc/eeprom/at24.c has support for nvmem though,
and MTD can be used as an nvmem provider too, so it's not clear to me
why we would want to create yet another variant.

But again, you shouldn't really ask me in the first place :)

I'm sure Miquel, Srinivas, and surely others, are much more relevant to
answer that question.

Maxime

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