Date: Wed, 5 Jun 2024 18:40:32 +0100
From: Conor Dooley <conor@...nel.org>
To: Michael Walle <mwalle@...nel.org>
Cc: Tudor Ambarus <tudor.ambarus@...aro.org>,
	Pratyush Yadav <pratyush@...nel.org>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-mtd@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Thorsten Scherer <t.scherer@...elmann.de>,
	Marek Vasut <marex@...x.de>, Imre Kaloz <kaloz@...nwrt.org>,
	Andrew Lunn <andrew@...n.ch>, Flavio Suligoi <f.suligoi@...m.it>
Subject: Re: [PATCH] dt-bindings: mtd: spi-nor: deprecate Everspin MRAM
 devices

On Tue, Jun 04, 2024 at 07:42:16PM +0200, Michael Walle wrote:
> On Tue Jun 4, 2024 at 7:01 PM CEST, Conor Dooley wrote:
> > On Tue, Jun 04, 2024 at 09:42:31AM +0200, Michael Walle wrote:
> > > These devices are more like an AT25 compatible EEPROM instead of
> > > flashes. Like an EEPROM the user doesn't need to explicitly erase the
> > > memory, nor are there sectors or pages. Thus, instead of the SPI-NOR
> > > (flash) driver, one should instead use the at25 EEPROM driver.
> > > 
> > > Signed-off-by: Michael Walle <mwalle@...nel.org>
> > > Cc: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > Cc: Thorsten Scherer <t.scherer@...elmann.de>
> > > Cc: Marek Vasut <marex@...x.de>
> > > Cc: Imre Kaloz <kaloz@...nwrt.org>
> > > Cc: Andrew Lunn <andrew@...n.ch>
> > > Cc: Flavio Suligoi <f.suligoi@...m.it>
> > > ---
> > > The referenced binding only supports the true AT25 compatible EEPROMs
> > > where you have to specify additional properties like size and page size
> > > or cypress FRAM devices where all the properties are discovered by the
> > > driver. I don't have the actual hardware, therefore I can't work on a
> > > proper driver and binding. But I really want to deprecate the use of
> > > these EEPROM like devices in SPI-NOR. So as a first step, mark the
> > > devices in the DT bindings as deprecated.
> > > 
> > > There are three in-tree users of this. I hope I've CCed all the relevant
> > > people. With the switch to the at25 driver also comes a user-space
> > > facing change: there is no more MTD device. Instead there is an "eeprom"
> > > file in /sys now, just like for every other EEPROM.
> > > 
> > > Marek already expressed, that the sps1 dts can likely be removed
> > > altogether. I'd like to hear from the other board DTS maintainers if
> > > they seem some problems moving to the EEPROM interface - or maybe that
> > > device isn't used at all anyway. So in the end, we can hopefully move
> > > all the users over to the at25 driver.
> > > ---
> > >  Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 9 ++++++++-
> > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> > > index 6e3afb42926e..2dccb6b049ea 100644
> > > --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> > > +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> > > @@ -21,7 +21,6 @@ properties:
> > >                (m25p(40|80|16|32|64|128)|\
> > >                n25q(32b|064|128a11|128a13|256a|512a|164k)))|\
> > >                atmel,at25df(321a|641|081a)|\
> > > -              everspin,mr25h(10|40|128|256)|\
> > >                (mxicy|macronix),mx25l(4005a|1606e|6405d|8005|12805d|25635e)|\
> > >                (mxicy|macronix),mx25u(4033|4035)|\
> > >                (spansion,)?s25fl(128s|256s1|512s|008k|064k|164k)|\
> > > @@ -42,6 +41,14 @@ properties:
> > >                - spansion,s25fs512s
> > >            - const: jedec,spi-nor
> > >        - const: jedec,spi-nor
> > > +
> > > +      # Deprecated bindings
> > > +      - items:
> > > +          - pattern: "^everspin,mr25h(10|40|128|256)$"
> > > +          - const: jedec,spi-nor
> > > +        description:
> > > +          Deprecated binding, use Documentation/devicetree/bindings/eeprom/at25.yaml.
> > > +        deprecated: true
> >
> > The idea here seems okay, but directing people to use the at25 binding,
> > without actually documenting the replacement compatibles etc is far from
> > ideal. I think even a wording change that points out that that these
> > devices need to be documented in that file would be an improvement, the
> > current wording makes it seem like the works been done.
> > Until there's a replacement driver, I don't think you could really
> > expect anyone to move to a new binding anyway.
> 
> Fair enough. The driver is already there and it basically works -
> Flavio is already using it. It is just, that at the moment you have
> to use the (deprecated) "atmel,at25" compatible and you'll have to
> specify pagesize etc. That is really hacky, because F/MRAM devices
> doesn't have a pagesize.
> 
> Anyway, I was already working on the at25 binding but then I've
> noticed that the current FRAM binding is really hardcoded to cypress
> devices and as mentioned in the commit message, I don't have any
> hardware to actually write the proper driver support. Maybe we
> should settle on the binding first, i.e.
> 
>  compatible = "everspin,mr25", "atmel,at25";
>  size = <N>;
> 
> vs
> 
>  compatible = "everspin,mr25h256"; # no size needed

I dunno, I am usually biased to having the more specific compatible
and not needing the extra properties.

> 
> For reference, the already supported cypress fram has the following:
> 
>  compatible = "cypress,fm25", "atmel,at25";
>  # no size needed, because the driver will figure it out by reading
>  # the ID
> 
> Besides that, I would really get some feedback from the three
> in-tree users on migrating to the EEPROM driver and thus away from
> MTD.
> 
> -michael
> 

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