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

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Date:   Wed, 4 Dec 2019 09:14:24 -0600
From:   Rob Herring <robh@...nel.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        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

On Fri, Nov 29, 2019 at 09:47:01AM +0100, Bartosz Golaszewski wrote:
> 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?

I agree with you. If it was called write-enable-gpios, then assert would 
be to enable writing.

Rob