linux-kernel - Re: [PATCH 1/4] dt-bindings: nvmem: new optional property write-protect-gpios

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Message-ID: <CAMpxmJU_0MzroyD_ZF5WOxpZz3dkADLOmW7aKpWdJ7GCvo-RnA@mail.gmail.com>
Date:   Fri, 22 Nov 2019 14:04:03 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Khouloud Touil <ktouil@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        baylibre-upstreaming@...ups.io,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, linux-i2c <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH 1/4] dt-bindings: nvmem: new optional property write-protect-gpios

pt., 22 lis 2019 o 13:53 Linus Walleij <linus.walleij@...aro.org> napisał(a):
>
> On Fri, Nov 22, 2019 at 1:47 PM Bartosz Golaszewski
> <bgolaszewski@...libre.com> wrote:
>
> > what about the existing bindings for at24 that don't mandate the
> > active-low flag? I'm afraid this would break the support for this
> > specific chip or lead to code duplication if we had this in both nvmem
> > and at24 with different logic.
>
> Hm yeah I realized this when I read patches 3 & 4.
>
> I would to like this:
>
> 1. Add a new generic property
>    writeprotect-gpios that mandates to use GPIO_ACTIVE_LOW
>    and use this in the new example
>
> 2. Deprecate wp-gpios in the binding, keep it around but deprecated.

This is a pretty standard property though - for instance it is
documented in the main mmc binding and doesn't mandate GPIO_ACTIVE_LOW
either. I think this is because nobody says that the write-protect
line must always be driver low to be asserted - this is highly
implementation-specific.

Bartosz

>
> 3. Add a quirk to gpiolib-of in the manner of the other quirks there
>    (like for SPI) so that if we are dealing with some EEPROM node
>    like at24 and the flag is zero, tag on GPIO_ACTIVE_LOW on
>    the descriptor.
>
> The driver will now handle the semantic of both cases
> with gpiolib-of providing a quirk for the old binding.
>
> This is how we solved this type of problem before.
>
> Yours,
> Linus Walleij