From patchwork Mon Feb 12 21:31:44 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Saravana Kannan X-Patchwork-Id: 772141 Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2AF784DA0F for ; Mon, 12 Feb 2024 21:32:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707773523; cv=none; b=lCAAjQeOe3Z4X9ArlF7yQCv5sEVdYtvab/DCI09N9HDNLPoKJgl1vUIVED/TJ+cDpmYfeqGMxqSPa5fNx3QBQcCQIDl8XYV1HAP491zos9wWY5quFz4vBiiOJLUIouP5DHYB/IiE/nOo05PvOw3Pbet8yoiduAuHDM46LA5OGek= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707773523; c=relaxed/simple; bh=dessp0Y0iydAOQinVxc9bvgHWYMKmwFPgKm6nVqH9Cs=; h=Date:In-Reply-To:Message-Id:Mime-Version:References:Subject:From: To:Cc:Content-Type; b=pHtHV3YG8967klfGvXNc2l/OomfIfrd93vQyzyWMn9lrCCJmuOlds2V0quQ+8vhd6zgdPOjKmoDjybmtqKeuscxsKBLcsdhx4d3HEB/+KF0afYE+LvEIt7en4L5eTwGsPFVGVyO9bYPU9Pvc91h/JtM3g3eIzxNaC4CpAfciP/4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--saravanak.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=K7SzWMdv; arc=none smtp.client-ip=209.85.219.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--saravanak.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="K7SzWMdv" Received: by mail-yb1-f201.google.com with SMTP id 3f1490d57ef6-dc6dbdcfd39so7579883276.2 for ; Mon, 12 Feb 2024 13:32:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1707773521; x=1708378321; darn=vger.kernel.org; h=cc:to:from:subject:references:mime-version:message-id:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=JQ35JcQOD8sngOY/PRE6LAzcrcvofp80cB9j/4A7v3U=; b=K7SzWMdvmea3hjbDgaKsjraad4vgI0rdi715XseSAT2erL0qicZ+OJQbMwTxgTW8IA 3JVBEOyTlCqlKTiZHu8uuXGEU/cV/e9e2nVpRIRhrpIHWVnn5W+NQIgKrtJc9mITwzVO FBZU5IoogTq2BMhQTG52HG5W0IMS4+zGrCe4vzcm2kaNwVRUFxvJJxJKh2LRahtyqgSe 4dNIb0eULHWrrWPVz1PgnoTrkJ71wAw4dAPviyCzJFuw/AzBDWRQeCQyKyKD3X8o/PvR sYJLPDW7F8Mv4e30ejWAxObfa0eKPJ9wcuZ+1DGHFT455OCyXsXQbL+aIN6XJK1z5J9d 3x+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707773521; x=1708378321; h=cc:to:from:subject:references:mime-version:message-id:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=JQ35JcQOD8sngOY/PRE6LAzcrcvofp80cB9j/4A7v3U=; b=MHV2HZt3up+Qwneur4VGy3SYHfPvdB21w3FOd8QxzxpcIiYpuc6SdkBrcb9G9S/Z5a B8OZzZ3/P1EqiC4k4g0QWDvMoNBrlidkP0ZaGojES0dg1o8Nf9+aYR3GxfviZtr2PoXf pPDJ7XaBAgvJb8qw37dxxPZYw0oqDK8155q69ERozbFinNrvatp60mVA6IYS9hnheNBV faU5Sr+ljZlBzRAa3la1TUFPb8xN/ikyfMLg9x+kIYkyYKsxrlLzOwBspLAyRaLJfJfE NOm1lr42NO/fZdmthSmvCifS/dXnLy/vcCnsBh9fxROFQP9qdv4XM5vz42/aW0e0vBjR f46g== X-Gm-Message-State: AOJu0YwhnWqcTNj+C8PtuFfGTLP6AbkjJCai2ISC7ZQ//z0NIzR9p1TG vRRtar6PUI+vdmQB5FTCA7JTIUdVrS67jY0jwf3MkCCVLUSGTkJuCb58Fsrt3fcM1dohBr8DBXf bO2CWtgPq5RjwEA== X-Google-Smtp-Source: AGHT+IHrNTiOANFi6Wik/igA8DAgLlLqlmFQTuxh1SYfHdUxTWNn7OObp7z0Jf+9QFwAM3tEUCLtAp8BPCqfywE= X-Received: from saravanak.san.corp.google.com ([2620:15c:2d:3:496d:5de1:a404:8bee]) (user=saravanak job=sendgmr) by 2002:a25:6910:0:b0:dc2:398d:a671 with SMTP id e16-20020a256910000000b00dc2398da671mr2027894ybc.10.1707773521205; Mon, 12 Feb 2024 13:32:01 -0800 (PST) Date: Mon, 12 Feb 2024 13:31:44 -0800 In-Reply-To: <20240212213147.489377-1-saravanak@google.com> Message-Id: <20240212213147.489377-4-saravanak@google.com> Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240212213147.489377-1-saravanak@google.com> X-Mailer: git-send-email 2.43.0.687.g38aa6559b0-goog Subject: [PATCH v2 3/4] dt-bindings: Add post-init-supplier property From: Saravana Kannan To: Saravana Kannan , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Greg Kroah-Hartman , "Rafael J. Wysocki" , Ard Biesheuvel , Frank Rowand , Len Brown , Andy Shevchenko , Daniel Scally , Heikki Krogerus , Sakari Ailus Cc: kernel-team@android.com, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-efi@vger.kernel.org, linux-acpi@vger.kernel.org The post-init-supplier property can be used to break a dependency cycle by marking some supplier(s) as a post device initialization supplier(s). This allows an OS to do a better job at ordering initialization and suspend/resume of the devices in a dependency cycle. Signed-off-by: Saravana Kannan --- .../bindings/post-init-supplier.yaml | 101 ++++++++++++++++++ MAINTAINERS | 13 +-- 2 files changed, 108 insertions(+), 6 deletions(-) create mode 100644 Documentation/devicetree/bindings/post-init-supplier.yaml diff --git a/Documentation/devicetree/bindings/post-init-supplier.yaml b/Documentation/devicetree/bindings/post-init-supplier.yaml new file mode 100644 index 000000000000..aab75b667259 --- /dev/null +++ b/Documentation/devicetree/bindings/post-init-supplier.yaml @@ -0,0 +1,101 @@ +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +# Copyright (c) 2020, Google LLC. All rights reserved. +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/post-init-supplier.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Post device initialization supplier + +maintainers: + - Saravana Kannan + +description: | + This property is used to indicate that the device(s) pointed to by the + property are not needed for the initialization of the device that lists this + property. This property is meaningful only when pointing to direct suppliers + of a device that are pointed to by other properties in the device. + + A device can list its suppliers in devicetree using one or more of the + standard devicetree bindings. By default, it would be safe to assume the + supplier device can be initialized before the consumer device is initialized. + + However, that assumption cannot be made when there are cyclic dependencies + between devices. Since each device is a supplier (directly or indirectly) of + the others in the cycle, there is no guaranteed safe order for initializing + the devices in a cycle. We can try to initialize them in an arbitrary order + and eventually successfully initialize all of them, but that doesn't always + work well. + + For example, say, + * The device tree has the following cyclic dependency X -> Y -> Z -> X (where + -> denotes "depends on"). + * But X is not needed to fully initialize Z (X might be needed only when a + specific functionality is requested post initialization). + + If all the other -> are mandatory initialization dependencies, then trying to + initialize the devices in a loop (or arbitrarily) will always eventually end + up with the devices being initialized in the order Z, Y and X. + + However, if Y is an optional supplier for X (where X provides limited + functionality when Y is not initialized and providing its services), then + trying to initialize the devices in a loop (or arbitrarily) could end up with + the devices being initialized in the following order: + + * Z, Y and X - All devices provide full functionality + * Z, X and Y - X provides partial functionality + * X, Z and Y - X provides partial functionality + + However, we always want to initialize the devices in the order Z, Y and X + since that provides the full functionality without interruptions. + + One alternate option that might be suggested is to have the driver for X + notice that Y became available at a later point and adjust the functionality + it provides. However, other userspace applications could have started using X + with the limited functionality before Y was available and it might not be + possible to transparently transition X or the users of X to full + functionality while X is in use. + + Similarly, when it comes to suspend (resume) ordering, it's unclear which + device in a dependency cycle needs to be suspended/resumed first and trying + arbitrary orders can result in system crashes or instability. + + Explicitly calling out which link in a cycle needs to be broken when + determining the order, simplifies things a lot, improves efficiency, makes + the behavior more deterministic and maximizes the functionality that can be + provided without interruption. + + This property is used to provide this additional information between devices + in a cycle by telling which supplier(s) is not needed for initializing the + device that lists this property. + + In the example above, Z would list X as a post-init-supplier and the + initialization dependency would become X -> Y -> Z -/-> X. So the best order + to initialize them become clear: Z, Y and then X. + +select: true +properties: + post-init-supplier: + # One or more suppliers can be marked as post initialization supplier + description: + List of phandles to suppliers that are not needed for initializing or + resuming this device. + $ref: /schemas/types.yaml#/definitions/phandle-array + items: + maxItems: 1 + +examples: + - | + gcc: clock-controller@1000 { + compatible = "vendor,soc4-gcc", "vendor,soc1-gcc"; + reg = <0x1000 0x80>; + clocks = <&dispcc 0x1> + #clock-cells = <1>; + post-init-supplier = <&dispcc>; + }; + dispcc: clock-controller@2000 { + compatible = "vendor,soc4-dispcc", "vendor,soc1-dispcc"; + reg = <0x2000 0x80>; + clocks = <&gcc 0xdd> + #clock-cells = <1>; + }; diff --git a/MAINTAINERS b/MAINTAINERS index 3dfe7ea25320..79719af714be 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -6055,12 +6055,6 @@ S: Maintained F: drivers/base/devcoredump.c F: include/linux/devcoredump.h -DEVICE DEPENDENCY HELPER SCRIPT -M: Saravana Kannan -L: linux-kernel@vger.kernel.org -S: Maintained -F: scripts/dev-needs.sh - DEVICE DIRECT ACCESS (DAX) M: Dan Williams M: Vishal Verma @@ -8295,6 +8289,13 @@ F: include/linux/firewire.h F: include/uapi/linux/firewire*.h F: tools/firewire/ +FIRMWARE DEVICE LINK (fw_devlink) +M: Saravana Kannan +L: linux-kernel@vger.kernel.org +S: Maintained +F: Documentation/devicetree/bindings/post-init-supplier.yaml +F: scripts/dev-needs.sh + FIRMWARE FRAMEWORK FOR ARMV8-A M: Sudeep Holla L: linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)