linux-kernel - Re: Getting at gpio- and pinctrl-devices as a consumer

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Message-ID: <CACRpkdb0cdvxgnuOBNfdY+idVcTXMwzKRYfCsFpiRx2qaVrt=w@mail.gmail.com>
Date:   Fri, 25 Nov 2016 00:29:40 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Alexandre Courbot <gnurou@...il.com>,
        Wolfram Sang <wsa-dev@...g-engineering.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Peter Korsgaard <peter.korsgaard@...co.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: Getting at gpio- and pinctrl-devices as a consumer

On Thu, Nov 24, 2016 at 10:35 PM, Peter Rosin <peda@...ntia.se> wrote:

> The background is that the gpio- and pinctrl-based i2c-mux drivers
> need to know if the device that is used to control the mux of the
> i2c-bus is also sitting on that very same i2c-bus. If it is, the
> locking has to be different and a bit more relaxed. This relaxed
> mode cannot be used always, as that would change the mux behavior
> in an unacceptable way for stuff expecting the (traditional)
> stricter locking. See Documentation/i2c/i2c-topology for more
> details if you need it.
>
> To check this, the i2c mux drivers dig out the device connected to
> each gpio-pin (or pinctrl-state) and walks up the device tree to see
> if the root i2c adapter that is muxed is in the loop.
>
> When I wrote this code, I could not find a clean way to go from a
> struct gpio_desc * to the relevant device, short of doing
>
>         #include "../../gpio/gpiolib.h"
>
>         gpio_dev = &gpio_desc->gdev->dev;
>
> And similarly for pinctrl:
>
>         #include "../../pinctrl/core.h"
>
>         struct pinctrl_setting *setting;
>         pinctrl_dev = setting->pctldev->dev;
>
> I'm not very proud of that, and wonder if there is a better way
> to get at the needed struct device? If not, then perhaps there
> should be?

Surely if I can be convinced that we need helpers for this
in GPIO and/or pin control we can add them.

They just need to be named something reasonable and
be generally useful for other situations of similar nature.

struct device *gpiod_get_backing_device(struct gpio_desc *d);

Is simple but is it really what you want?

Yours,
Linus Walleij