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

[Marek Vasut <marex@nabladev.com>]

On 4/24/26 10:12 AM, Bartosz Golaszewski wrote:
> On Thu, Apr 23, 2026 at 9:15 PM Marek Vasut <marex@nabladev.com> wrote:
>>
>> On 4/23/26 4:19 PM, Bartosz Golaszewski wrote:
>>> On Thu, Apr 23, 2026 at 4:06 PM Marek Vasut <marex@nabladev.com> wrote:
>>>>
>>>> On 4/23/26 2:17 PM, Bartosz Golaszewski wrote:
>>>>> On Thu, Apr 23, 2026 at 2:04 PM Marek Vasut <marex@nabladev.com> 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.