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

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Message-ID: <20240823173748.2b3a364a@xps-13>
Date: Fri, 23 Aug 2024 17:37:48 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Marco Felsch <m.felsch@...gutronix.de>
Cc: Maxime Ripard <mripard@...nel.org>, Pratyush Yadav
 <pratyush@...nel.org>, Tudor Ambarus <tudor.ambarus@...aro.org>, Richard
 Weinberger <richard@....at>, Vignesh Raghavendra <vigneshr@...com>, Arnd
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 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>,
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 Andrew Lunn <andrew@...n.ch>, Gregory Clement
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 Jonathan Neuschäfer <j.neuschaefer@....net>, Michael
 Ellerman <mpe@...erman.id.au>, 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,
 linux-renesas-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
 openbmc@...ts.ozlabs.org, linuxppc-dev@...ts.ozlabs.org,
 linux-mips@...r.kernel.org, loongarch@...ts.linux.dev, Michael Walle
 <michael@...le.cc>
Subject: Re: [PATCH 4/9] mtd: devices: add AT24 eeprom support

Hi Marco,

m.felsch@...gutronix.de wrote on Thu, 18 Jul 2024 11:17:53 +0200:

> Hi Miquel,
> 
> On 24-07-17, Miquel Raynal wrote:
> > Hi Marco,
> >   
> > > > > > Overall I think the idea of getting rid of these misc/ drivers is goes
> > > > > > into the right direction, but registering directly into NVMEM makes
> > > > > > more sense IMO.      
> > > > > 
> > > > > So you propose to have two places for the partition handling (one for
> > > > > MTD and one for NVMEM) instead of one and moving the code into NVMEM
> > > > > directly?    
> > > > 
> > > > Why two places for the partitions handling? Just one, in NVMEM. Also    
> > > 
> > > Without checking the details I think that converting the MTD
> > > partitioning code into NVMEM partitioning code is a bigger task. As you
> > > said below there are many legacy code paths you need to consider so they
> > > still work afterwards as well.
> > >   
> > > > usually EEPROMs don't require very advanced partitioning schemes,
> > > > unlike flashes (which are the most common MTD devices today).    
> > > 
> > > As said in my cover letter EEPROMs can become quite large and MTD
> > > supports partitioning storage devices which is very handy for large
> > > EEPROMs as well.  
> > 
> > Did you had a look at nvmem-layouts ? In particular the fixed-layout.  
> 
> Yes I had a look at nvmem-layouts and we use them within a
> mtd-partition. Using them instead of a mtd-partition is not sufficient
> since they:
>  1) don't support user-space write (I send a patch for it but it doesn't
>     seem to be accepted soon).

Yes, this needed improvements maybe but was not refused either.

>  2) If write would be supported the user-space need to write the
>     complete cell e.g. no partial writes.

Maybe that can also be brought to nvmem. Again, nvmem was introduced
for handling EEPROMs in the first place.

Anyway, if other people in Cc: want to share some thoughts, they are
also welcomed, I don't want to block this series for bad reasons. I'm
also adding Michael Walle in Cc: who might have an opinion on that.

Link: https://lore.kernel.org/linux-mtd/20240701-b4-v6-10-topic-usbc-tcpci-v1-4-3fd5f4a193cc@pengutronix.de/

Thanks,
Miquèl