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

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Message-ID: <CACRpkdaZrvPObjyN4kasARzKZ9=PiAcvTzXzWkmC7R+Ay5tU8w@mail.gmail.com>
Date:   Fri, 22 Nov 2019 13:41:08 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Khouloud Touil <ktouil@...libre.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...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

Hi Khouloud,

thanks for your patch!

I just have a semantic comment:

On Wed, Nov 20, 2019 at 3:21 PM Khouloud Touil <ktouil@...libre.com> wrote:

> Instead of modifying all the memory drivers to check this pin, make
> the NVMEM subsystem check if the write-protect GPIO being passed
> through the nvmem_config or defined in the device tree and pull it
> low whenever writing to the memory.

It is claimed that this should be pulled low to assert it so by
definition it is active low.

> +  wp-gpios:
> +    description:
> +      GPIO to which the write-protect pin of the chip is connected.
> +    maxItems: 1

Mandate that the flag in the second cell should be GPIO_ACTIVE_LOW

>  patternProperties:
>    "^.*@[0-9a-f]+$":
>      type: object
> @@ -66,6 +71,7 @@ examples:
>        qfprom: eeprom@...000 {
>            #address-cells = <1>;
>            #size-cells = <1>;
> +          wp-gpios = <&gpio1 3 0>;

#include <dt-bindings/gpio/gpio.h>
wp-gpios = <&gpio1 3 GPIO_ACTIVE_LOW>;

This will in Linux have the semantic effect that you need to
set the output high with gpio_set_val(d, 1) to assert it
(drive it low) but that really doesn't matter to the device tree
bindings, those are OS-agnostic: if the line is active low then
it should use this flag.

It has the upside that the day you need a write-protect that
is active high, it is simple to support that use case too.

Yours,
Linus Walleij