From patchwork Mon May 11 14:52:56 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Geert Uytterhoeven X-Patchwork-Id: 1287851 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=glider.be 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 ozlabs.org (Postfix) with ESMTPS id 49LPBq03brz9sPF for ; Tue, 12 May 2020 00:56:03 +1000 (AEST) Received: from localhost ([::1]:53112 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jY9qa-00033g-NM for incoming@patchwork.ozlabs.org; Mon, 11 May 2020 10:56:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34506) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jY9nx-0004yB-Bg for qemu-devel@nongnu.org; Mon, 11 May 2020 10:53:18 -0400 Received: from xavier.telenet-ops.be ([2a02:1800:120:4::f00:14]:49174) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jY9nt-0000dk-4K for qemu-devel@nongnu.org; Mon, 11 May 2020 10:53:17 -0400 Received: from ramsan ([IPv6:2a02:1810:ac12:ed60:702c:fb99:3097:2049]) by xavier.telenet-ops.be with bizsmtp id dSsy2200A0GoAb601SsyQe; Mon, 11 May 2020 16:53:09 +0200 Received: from rox.of.borg ([192.168.97.57]) by ramsan with esmtp (Exim 4.90_1) (envelope-from ) id 1jY9ne-00082p-6p; Mon, 11 May 2020 16:52:58 +0200 Received: from geert by rox.of.borg with local (Exim 4.90_1) (envelope-from ) id 1jY9ne-0005zd-5G; Mon, 11 May 2020 16:52:58 +0200 From: Geert Uytterhoeven To: Linus Walleij , Bartosz Golaszewski , Jonathan Corbet , Harish Jenny K N , Eugeniu Rosca Subject: [PATCH v7 5/6] docs: gpio: Add GPIO Aggregator documentation Date: Mon, 11 May 2020 16:52:56 +0200 Message-Id: <20200511145257.22970-6-geert+renesas@glider.be> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200511145257.22970-1-geert+renesas@glider.be> References: <20200511145257.22970-1-geert+renesas@glider.be> Received-SPF: none client-ip=2a02:1800:120:4::f00:14; envelope-from=geert@linux-m68k.org; helo=xavier.telenet-ops.be X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_LOW=-0.7, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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: 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, Alexander Graf , Paolo Bonzini , Phil Reid Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.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 --- v7: - No changes, 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