From: Ulrich Hecht <uli@fpond.eu>
To: Geert Uytterhoeven <geert+renesas@glider.be>,
Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Jonathan Corbet <corbet@lwn.net>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Harish Jenny K N <harish_kandiga@mentor.com>,
Eugeniu Rosca <erosca@de.adit-jv.com>
Cc: Alexander Graf <graf@amazon.com>,
Peter Maydell <peter.maydell@linaro.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Phil Reid <preid@electromag.com.au>,
Marc Zyngier <marc.zyngier@arm.com>,
Christoffer Dall <christoffer.dall@arm.com>,
Magnus Damm <magnus.damm@gmail.com>,
linux-gpio@vger.kernel.org, linux-doc@vger.kernel.org,
devicetree@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
linux-kernel@vger.kernel.org, qemu-devel@nongnu.org
Subject: Re: [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation
Date: Thu, 28 Nov 2019 04:41:02 +0100 (CET) [thread overview]
Message-ID: <761320534.1467709.1574912462950@webmail.strato.com> (raw)
In-Reply-To: <20191127084253.16356-7-geert+renesas@glider.be>
> On November 27, 2019 at 9:42 AM Geert Uytterhoeven <geert+renesas@glider.be> wrote:
>
>
> Document the GPIO Aggregator/Repeater, and the three typical use-cases.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> v3:
> - New.
> ---
> .../admin-guide/gpio/gpio-aggregator.rst | 111 ++++++++++++++++++
> Documentation/admin-guide/gpio/index.rst | 1 +
> 2 files changed, 112 insertions(+)
> create mode 100644 Documentation/admin-guide/gpio/gpio-aggregator.rst
>
> diff --git a/Documentation/admin-guide/gpio/gpio-aggregator.rst b/Documentation/admin-guide/gpio/gpio-aggregator.rst
> new file mode 100644
> index 0000000000000000..826146e260253299
> --- /dev/null
> +++ b/Documentation/admin-guide/gpio/gpio-aggregator.rst
> @@ -0,0 +1,111 @@
> +.. SPDX-License-Identifier: GPL-2.0-only
> +
> +GPIO Aggregator/Repeater
> +========================
> +
> +The GPIO Aggregator/Repeater allows to aggregate GPIOs, and expose them as a
> +new gpio_chip. This supports the following use cases.
> +
> +
> +Aggregating GPIOs using Sysfs
> +-----------------------------
> +
> +GPIO controllers are exported to userspace using /dev/gpiochip* character
> +devices. Access control to these devices is provided by standard UNIX file
> +system permissions, on an all-or-nothing basis: either a GPIO controller is
> +accessible for a user, or it is not.
> +
> +The GPIO Aggregator allows access control for individual GPIOs, by aggregating
> +them into a new gpio_chip, which can be assigned to a group or user using
> +standard UNIX file ownership and permissions. Furthermore, this simplifies and
> +hardens exporting GPIOs to a virtual machine, as the VM can just grab the full
> +GPIO controller, and no longer needs to care about which GPIOs to grab and
> +which not, reducing the attack surface.
> +
> +Aggregated GPIO controllers are instantiated and destroyed by writing to
> +write-only attribute files in sysfs.
> +
> + /sys/bus/platform/drivers/gpio-aggregator/
> +
> + "new_device" ...
> + Userspace may ask the kernel to instantiate an aggregated GPIO
> + controller by writing a string describing the GPIOs to
> + aggregate to the "new_device" file, using the format
> +
> + .. code-block:: none
> +
> + [<gpioA>] [<gpiochipB> <offsets>] ...
> +
> + Where:
> +
> + "<gpioA>" ...
> + is a GPIO line name,
> +
> + "<gpiochipB>" ...
> + is a GPIO chip label or name, and
> +
> + "<offsets>" ...
> + is a comma-separated list of GPIO offsets and/or
> + GPIO offset ranges denoted by dashes.
> +
> + Example: Instantiate a new GPIO aggregator by aggregating GPIO
> + 19 of "e6052000.gpio" and GPIOs 20-21 of "gpiochip2" into a new
> + gpio_chip:
> +
> + .. code-block:: bash
> +
> + echo 'e6052000.gpio 19 gpiochip2 20-21' > new_device
> +
> + "delete_device" ...
> + Userspace may ask the kernel to destroy an aggregated GPIO
> + controller after use by writing its device name to the
> + "delete_device" file.
> +
> + Example: Destroy the previously-created aggregated GPIO
> + controller "gpio-aggregator.0":
> +
> + .. code-block:: bash
> +
> + echo gpio-aggregator.0 > delete_device
> +
> +
> +GPIO Repeater in Device Tree
> +----------------------------
> +
> +A GPIO Repeater is a node in a Device Tree representing a repeater for one or
> +more GPIOs, possibly including physical signal property translation (e.g.
> +polarity inversion). This allows to model e.g. inverters in DT.
> +
> +See Documentation/devicetree/bindings/gpio/gpio-repeater.yaml
> +
> +
> +Generic GPIO Driver
> +-------------------
> +
> +The GPIO Aggregator can also be used as a generic driver for a simple
> +GPIO-operated device described in DT, without a dedicated in-kernel driver.
> +This is not unlike e.g. spidev, which allows to communicated with an SPI device
> +from userspace.
> +
> +Binding a device to the GPIO Aggregator is performed either by modifying the
> +gpio-aggregator driver, or by writing to the "driver_override" file in Sysfs.
> +
> +Example: If "frobnicator" is a GPIO-operated device described in DT, using its
> +own compatible value::
> +
> + frobnicator {
> + compatible = "myvendor,frobnicator";
> +
> + gpios = <&gpio2 19 GPIO_ACTIVE_HIGH>,
> + <&gpio2 20 GPIO_ACTIVE_LOW>;
> + };
> +
> +it can be bound to the GPIO Aggregator by either:
> +
> +1. Adding its compatible value to ``gpio_aggregator_dt_ids[]``,
> +2. Binding manually using "driver_override":
> +
> +.. code-block:: bash
> +
> + echo gpio-aggregator > /sys/bus/platform/devices/frobnicator/driver_override
> + echo frobnicator > /sys/bus/platform/drivers/gpio-aggregator/bind
> diff --git a/Documentation/admin-guide/gpio/index.rst b/Documentation/admin-guide/gpio/index.rst
> index a244ba4e87d5398a..ef2838638e967777 100644
> --- a/Documentation/admin-guide/gpio/index.rst
> +++ b/Documentation/admin-guide/gpio/index.rst
> @@ -7,6 +7,7 @@ gpio
> .. toctree::
> :maxdepth: 1
>
> + gpio-aggregator
> sysfs
>
> .. only:: subproject and html
> --
> 2.17.1
>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
CU
Uli
next prev parent reply other threads:[~2019-11-28 3:47 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-27 8:42 [PATCH v3 0/7] gpio: Add GPIO Aggregator/Repeater Geert Uytterhoeven
2019-11-27 8:42 ` [PATCH v3 1/7] gpiolib: Add GPIOCHIP_NAME definition Geert Uytterhoeven
2019-11-28 3:38 ` Ulrich Hecht
2019-12-02 21:17 ` Eugeniu Rosca
2019-12-12 10:37 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 2/7] gpiolib: Add support for gpiochipN-based table lookup Geert Uytterhoeven
2019-11-28 3:38 ` Ulrich Hecht
2019-12-12 13:20 ` Linus Walleij
2019-12-12 13:33 ` Geert Uytterhoeven
2019-12-12 14:36 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 3/7] gpiolib: Add support for GPIO line " Geert Uytterhoeven
2019-11-28 3:39 ` Ulrich Hecht
2019-12-12 13:40 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 4/7] dt-bindings: gpio: Add gpio-repeater bindings Geert Uytterhoeven
2019-11-28 3:39 ` Ulrich Hecht
2019-12-03 5:51 ` Harish Jenny K N
2019-12-05 21:06 ` Rob Herring
2019-12-06 9:17 ` Geert Uytterhoeven
2019-12-06 15:03 ` Rob Herring
2020-01-06 8:12 ` Geert Uytterhoeven
2020-01-07 9:22 ` Harish Jenny K N
2020-01-16 5:09 ` Harish Jenny K N
2019-11-27 8:42 ` [PATCH v3 5/7] gpio: Add GPIO Aggregator/Repeater driver Geert Uytterhoeven
2019-11-27 14:15 ` Eugeniu Rosca
2019-11-27 14:33 ` Geert Uytterhoeven
2019-11-28 3:40 ` Ulrich Hecht
2019-12-03 5:42 ` Harish Jenny K N
2019-12-03 8:17 ` Geert Uytterhoeven
2019-12-03 8:51 ` Harish Jenny K N
2019-12-03 10:51 ` Eugeniu Rosca
2020-01-09 13:35 ` Geert Uytterhoeven
2020-01-09 13:49 ` Eugeniu Rosca
2019-12-12 14:34 ` Linus Walleij
2019-12-12 15:24 ` Geert Uytterhoeven
2020-01-04 0:38 ` Linus Walleij
2020-01-06 8:23 ` Geert Uytterhoeven
2020-01-08 23:12 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation Geert Uytterhoeven
2019-11-28 3:41 ` Ulrich Hecht [this message]
2019-12-12 14:42 ` Linus Walleij
2019-12-12 14:48 ` Geert Uytterhoeven
2020-01-04 0:21 ` Linus Walleij
2020-01-06 8:06 ` Geert Uytterhoeven
2019-11-27 8:42 ` [PATCH v3 7/7] MAINTAINERS: Add GPIO Aggregator/Repeater section Geert Uytterhoeven
2019-12-03 5:38 ` Harish Jenny K N
2020-01-18 1:46 ` [PATCH v3 0/7] gpio: Add GPIO Aggregator/Repeater Eugeniu Rosca
2020-01-20 9:33 ` Geert Uytterhoeven
2020-01-20 12:14 ` Eugeniu Rosca
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=761320534.1467709.1574912462950@webmail.strato.com \
--to=uli@fpond.eu \
--cc=bgolaszewski@baylibre.com \
--cc=christoffer.dall@arm.com \
--cc=corbet@lwn.net \
--cc=devicetree@vger.kernel.org \
--cc=erosca@de.adit-jv.com \
--cc=geert+renesas@glider.be \
--cc=graf@amazon.com \
--cc=harish_kandiga@mentor.com \
--cc=linus.walleij@linaro.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-gpio@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-renesas-soc@vger.kernel.org \
--cc=magnus.damm@gmail.com \
--cc=marc.zyngier@arm.com \
--cc=mark.rutland@arm.com \
--cc=pbonzini@redhat.com \
--cc=peter.maydell@linaro.org \
--cc=preid@electromag.com.au \
--cc=qemu-devel@nongnu.org \
--cc=robh+dt@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).