Re: [PATCH] dt-bindings: mtd: spi-nor: deprecate Everspin MRAM devices

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Hi,

removing Uwe from CC as this address bounces.

Am Freitag, 21. Juni 2024, 09:09:56 CEST schrieb Michael Walle:
> On Fri Jun 21, 2024 at 8:49 AM CEST, Alexander Stein wrote:
> > Hi everyone,
> >
> > sorry for being late to the party. I just noticed this discussion while
> > reading [1].
> >
> > Am Dienstag, 4. Juni 2024, 09:42:31 CEST schrieb Michael Walle:
> > > 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@kernel.org>
> > > Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > > Cc: Thorsten Scherer <t.scherer@eckelmann.de>
> > > Cc: Marek Vasut <marex@denx.de>
> > > Cc: Imre Kaloz <kaloz@openwrt.org>
> > > Cc: Andrew Lunn <andrew@lunn.ch>
> > > Cc: Flavio Suligoi <f.suligoi@asem.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.
> >
> > So instead of spi-nor you want to use at25 for this MRAM devices?
> 
> Yes.
> 
> > AFAICS at25 is a spi only driver, but spi-nor is a spi-mem driver. So I am
> > wondering if at25 driver is capable of using QSPI hosts.
> 
> spi-mem support could be added to the at25 driver. But probably
> mainly because there are SPI controllers out there which only have
> an interface to attach memory (like the FlexSPI from NXP).

Yes, FlexSPI is my current area of interest.

> > Everspin EMxxLXB devices are capable of running in xSPI modes.
> > Regarding QSPI (DSPI/OSPI as well) I assumed spi-nor is a given, but maybe
> > I am completely wrong here. Maybe someone could clarify this.
> 
> These newer devices should also support the erase command, right? So
> they can be a "real" flash. If they support SFDP, the would even be
> supported out of the box. The mentioned everspin devices are much
> older and behaves more like an EEPROM instead of a flash.

I see this is about older devices, I got misled by the subject.
The new devices EMxxLX devices do not support SFDP. There are erase commands,
but unless you want to set sectors/whole chip to a defined state, this seems
unneeded, so SPI_NOR_NO_ERASE would be sensible.
I'm wondering if the comment in [1] is still applicable unconditionally, as
there still is a use-case for spi-nor on flexspi.

Best regards,
Alexander

[1] https://lore.kernel.org/linux-kernel/D0C9NCOMI27O.2VW2U3FNFTSPK@kernel.org/
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