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

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Message-ID: <20240718091753.apwsrvmekn2vvo4k@pengutronix.de>
Date: Thu, 18 Jul 2024 11:17:53 +0200
From: Marco Felsch <m.felsch@...gutronix.de>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: Maxime Ripard <mripard@...nel.org>,
	Pratyush Yadav <pratyush@...nel.org>,
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Subject: Re: [PATCH 4/9] mtd: devices: add AT24 eeprom support

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

> Is there anything you would like to achieve already that is not
> possible with nvmem but is with mtd?

Please see above.

Regards,
  Marco