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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)
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

  reply index

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

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