From patchwork Wed Nov 27 08:42:52 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Geert Uytterhoeven X-Patchwork-Id: 1201438 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=linux-gpio-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=glider.be Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 47NDnY3GRyz9sSw for ; Wed, 27 Nov 2019 19:43:29 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726664AbfK0InZ (ORCPT ); Wed, 27 Nov 2019 03:43:25 -0500 Received: from andre.telenet-ops.be ([195.130.132.53]:43630 "EHLO andre.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726655AbfK0InL (ORCPT ); Wed, 27 Nov 2019 03:43:11 -0500 Received: from ramsan ([84.195.182.253]) by andre.telenet-ops.be with bizsmtp id Wwiu2100e5USYZQ01wiuXV; Wed, 27 Nov 2019 09:43:07 +0100 Received: from rox.of.borg ([192.168.97.57]) by ramsan with esmtp (Exim 4.90_1) (envelope-from ) id 1iZsuU-0000xt-QR; Wed, 27 Nov 2019 09:42:54 +0100 Received: from geert by rox.of.borg with local (Exim 4.90_1) (envelope-from ) id 1iZsuU-0004P0-Ny; Wed, 27 Nov 2019 09:42:54 +0100 From: Geert Uytterhoeven To: Linus Walleij , Bartosz Golaszewski , Jonathan Corbet , Rob Herring , Mark Rutland , Harish Jenny K N , Eugeniu Rosca Cc: Alexander Graf , Peter Maydell , Paolo Bonzini , Phil Reid , Marc Zyngier , Christoffer Dall , Magnus Damm , 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, Geert Uytterhoeven Subject: [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation Date: Wed, 27 Nov 2019 09:42:52 +0100 Message-Id: <20191127084253.16356-7-geert+renesas@glider.be> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191127084253.16356-1-geert+renesas@glider.be> References: <20191127084253.16356-1-geert+renesas@glider.be> Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org Document the GPIO Aggregator/Repeater, and the three typical use-cases. Signed-off-by: Geert Uytterhoeven Reviewed-by: Ulrich Hecht --- 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 + + [] [ ] ... + + Where: + + "" ... + is a GPIO line name, + + "" ... + is a GPIO chip label or name, and + + "" ... + 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