From patchwork Tue Mar 24 13:56:52 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Geert Uytterhoeven X-Patchwork-Id: 11455549 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 3B95D174A for ; Tue, 24 Mar 2020 13:59:57 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1C3CE205ED for ; Tue, 24 Mar 2020 13:59:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1C3CE205ED Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=glider.be Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:49292 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jGk60-0004yY-AM for patchwork-qemu-devel@patchwork.kernel.org; Tue, 24 Mar 2020 09:59:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53311) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jGk3K-000062-VS for qemu-devel@nongnu.org; Tue, 24 Mar 2020 09:57:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jGk3J-0006Gt-8H for qemu-devel@nongnu.org; Tue, 24 Mar 2020 09:57:10 -0400 Received: from albert.telenet-ops.be ([2a02:1800:110:4::f00:1a]:55114) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1jGk3I-0006CU-It for qemu-devel@nongnu.org; Tue, 24 Mar 2020 09:57:08 -0400 Received: from ramsan ([84.195.182.253]) by albert.telenet-ops.be with bizsmtp id JDwu2200T5USYZQ06DwuaB; Tue, 24 Mar 2020 14:57:06 +0100 Received: from rox.of.borg ([192.168.97.57]) by ramsan with esmtp (Exim 4.90_1) (envelope-from ) id 1jGk34-0006Ot-OI; Tue, 24 Mar 2020 14:56:54 +0100 Received: from geert by rox.of.borg with local (Exim 4.90_1) (envelope-from ) id 1jGk34-0001ko-MP; Tue, 24 Mar 2020 14:56:54 +0100 From: Geert Uytterhoeven To: Linus Walleij , Bartosz Golaszewski , Jonathan Corbet , Harish Jenny K N , Eugeniu Rosca Subject: [PATCH v6 7/8] docs: gpio: Add GPIO Aggregator documentation Date: Tue, 24 Mar 2020 14:56:52 +0100 Message-Id: <20200324135653.6676-7-geert+renesas@glider.be> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200324135653.6676-1-geert+renesas@glider.be> References: <20200324135328.5796-1-geert+renesas@glider.be> <20200324135653.6676-1-geert+renesas@glider.be> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 2a02:1800:110:4::f00:1a X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Peter Maydell , qemu-devel@nongnu.org, Geert Uytterhoeven , linux-doc@vger.kernel.org, Marc Zyngier , Magnus Damm , Christoffer Dall , linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-gpio@vger.kernel.org, Rob Herring , Alexander Graf , Paolo Bonzini , Phil Reid Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" Document the GPIO Aggregator, and the two typical use-cases. Signed-off-by: Geert Uytterhoeven Reviewed-by: Ulrich Hecht Reviewed-by: Eugeniu Rosca Tested-by: Eugeniu Rosca --- v6: - Fix "allows" without object: -> provides a mechanism to aggregate GPIOs, -> provides access control for a set of one or more GPIOs, -> allows the user to communicate, - Drop "gpiochipN" support, - Extend example, v5: - Add Reviewed-by, Tested-by, - Fix inconsistent indentation, v4: - Add Reviewed-by, - Drop controversial GPIO repeater, - Clarify industrial control use case, - Fix typo s/communicated/communicate/, - Replace abstract frobnicator example by concrete door example with gpio-line-names, 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..5cd1e7221756504c --- /dev/null +++ b/Documentation/admin-guide/gpio/gpio-aggregator.rst @@ -0,0 +1,111 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +GPIO Aggregator +=============== + +The GPIO Aggregator provides a mechanism 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 provides access control for a set of one or more 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, 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 + line 19 of "e6052000.gpio" and GPIO lines 20-21 of + "e6050000.gpio" into a new gpio_chip: + + .. code-block:: sh + + $ echo 'e6052000.gpio 19 e6050000.gpio 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, assumed to be "gpio-aggregator.0": + + .. code-block:: sh + + $ echo gpio-aggregator.0 > delete_device + + +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 useful in industrial control, and is not unlike e.g. spidev, which +allows the user to communicate 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 "door" is a GPIO-operated device described in DT, using its own +compatible value:: + + door { + compatible = "myvendor,mydoor"; + + gpios = <&gpio2 19 GPIO_ACTIVE_HIGH>, + <&gpio2 20 GPIO_ACTIVE_LOW>; + gpio-line-names = "open", "lock"; + }; + +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:: sh + + $ echo gpio-aggregator > /sys/bus/platform/devices/door/driver_override + $ echo door > /sys/bus/platform/drivers/gpio-aggregator/bind + +After that, a new gpiochip "door" has been created: + +.. code-block:: sh + + $ gpioinfo door + gpiochip12 - 2 lines: + line 0: "open" unused input active-high + line 1: "lock" unused input active-high 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