Re: [PATCH] nvmem: core: eeprom: at24: Handle EEPROM with both read-only and wp-gpios

[Marek Vasut]

On 4/24/26 10:12 AM, Bartosz Golaszewski wrote:
> On Thu, Apr 23, 2026 at 9:15 PM Marek Vasut <marex@xxxxxxxxxxxx> wrote:
> > On 4/23/26 4:19 PM, Bartosz Golaszewski wrote:
> > > On Thu, Apr 23, 2026 at 4:06 PM Marek Vasut <marex@xxxxxxxxxxxx> wrote:
> > > > On 4/23/26 2:17 PM, Bartosz Golaszewski wrote:
> > > > > On Thu, Apr 23, 2026 at 2:04 PM Marek Vasut <marex@xxxxxxxxxxxx> wrote:
> > > > > > > I see. Ok, please send a v2.
> > > > > > Does this patch require any changes ?
> > > > > >
> > > > > > I will be sending the DT changes separately.
> > > > >
> > > > > Sashiko is saying this:
> > > > > https://sashiko.dev/#/patchset/20260421140755.54222-1-marex%40nabladev.com
> > > >
> > > > What does this mean ?
> > > >
> > > > > Shouldn't we report the device as read-only in sysfs unless it was
> > > > > "unlocked" with force_ro?
> > > > This would be ideal, but I did not find a way to toggle the "nvmem" bin
> > > > attr permissions at runtime. Is that even possible ?
> > >
> > > Right, it seems like it's set once and can't be changed (Greg: correct
> > > me if I'm wrong).
> > >
> > > Ok, nevermind the comment then. Maybe just split the changes into
> > > nvmem and at24 changes and I can take both with an Ack from Srini.
> > I have two more ideas I would like to run past you ... how about either:
> >
> > - If wp-gpios is present, set the device as default RO after boot, and
>
> Isn't this already what happens though? nvmem core requests the GPIO
> as output-high and drives it low only when it's doing the writing.

It isn't, the default is read-write . But I now submitted a V2:

nvmem: core: Default to read-only if wp-gpios present

> >     let force_ro sysfs attribute toggle the protection of the device back
> >     and forth afterward. This would however change the userspace facing
> >     behavior slightly, because right now, with wp-gpios present in DT, the
> >     device is default RW.
>
> Or do you mean just the file permissions?
>
> If the latter, then that does sound logically sound but yeah, it's
> asking for a regression report. :)

Please see "nvmem: core: Default to read-only if wp-gpios present" that 
I just submitted.

> > - Introduce new DT property, wp-gpios-default-read-only or
> >     default-read-only or some such, to indicate the device should be in
> >     read-only mode by default. That would mitigate the downside of the
> >     aforementioned point, but would require a new DT property.
> >
> > Thoughts ?
>
> I like "default-read-only" and it both allows to introduce this
> behavior and not break existing users. Let's loop in DT maintainers
> and see. I'd just like to clarify if we're talking about sysfs
> permissions or GPIO behavior here.
I think we might not need this, please see above.