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

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Date:   Fri, 29 Nov 2019 09:47:01 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Khouloud Touil <ktouil@...libre.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        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

czw., 28 lis 2019 o 14:45 Linus Walleij <linus.walleij@...aro.org> napisał(a):
>
> On Tue, Nov 26, 2019 at 4:18 PM Khouloud Touil <ktouil@...libre.com> wrote:
>
> > [Me]
> >> 4. The code still need to be modified to set the value
> >>    to "1" to assert the line since the gpiolib now handles
> >>    the inversion semantics.
>
> > By saying "assert the wp" do you mean enable the write operation or
> > block it ?
>
> Yeah one more layer of confusion, sorry :/
>
> By "asserting WP" I mean driving the line to a state where
> writing to the EEPROM is enabled, i.e. the default state is
> that the EEPROM is write protected and when you "assert"
> WP it becomes writable.
>
> If you feel the inverse semantics are more intuitive (such that
> WP comes up asserted and thus write protected), be my
> guest :D
>

Ha! I've always assumed that "to assert the write-protect pin" means
to *protect* the EEPROM from writing. That's why it comes up as
asserted (logical '1' in the driver) and we need to deassert it (drive
it low, logical '0' in the driver) to enable writing. This is the
current behavior and I'd say in this case it's just a matter of very
explicit statement that this is how it works in the DT binding?

Rob: any thoughts on this?

Bartosz

> As long as it is unambiguously documented in the bindings
> and with comments in the code I'm game for whatever the
> at24 people feel is most appropriate. (You will set the standard
> for everyone else.)
>
> Yours.
> Linus Walleij