From patchwork Tue Nov 19 16:12:12 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Leonard Crestez X-Patchwork-Id: 11252409 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 BD6B213A4 for ; Tue, 19 Nov 2019 16:13:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A7327223AE for ; Tue, 19 Nov 2019 16:13:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728475AbfKSQNE (ORCPT ); Tue, 19 Nov 2019 11:13:04 -0500 Received: from inva020.nxp.com ([92.121.34.13]:41628 "EHLO inva020.nxp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728470AbfKSQNE (ORCPT ); Tue, 19 Nov 2019 11:13:04 -0500 Received: from inva020.nxp.com (localhost [127.0.0.1]) by inva020.eu-rdc02.nxp.com (Postfix) with ESMTP id 33C351A000D; Tue, 19 Nov 2019 17:13:01 +0100 (CET) Received: from inva024.eu-rdc02.nxp.com (inva024.eu-rdc02.nxp.com [134.27.226.22]) by inva020.eu-rdc02.nxp.com (Postfix) with ESMTP id 270F91A0065; Tue, 19 Nov 2019 17:13:01 +0100 (CET) Received: from fsr-ub1864-112.ea.freescale.net (fsr-ub1864-112.ea.freescale.net [10.171.82.98]) by inva024.eu-rdc02.nxp.com (Postfix) with ESMTP id 3E43D2039B; Tue, 19 Nov 2019 17:13:00 +0100 (CET) From: Leonard Crestez To: Chanwoo Choi , Matthias Kaehlcke , "Rafael J. Wysocki" Cc: Kyungmin Park , MyungJoo Ham , =?utf-8?b?QXJ0dXIgxZp3aWdvxYQ=?= , Saravana Kannan , Krzysztof Kozlowski , Alexandre Bailon , Georgi Djakov , Jacky Bai , Viresh Kumar , NXP Linux Team , linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH RFC 0/2] PM / devfreq: Add dev_pm_qos support with minimal changes Date: Tue, 19 Nov 2019 18:12:12 +0200 Message-Id: X-Mailer: git-send-email 2.17.1 X-Virus-Scanned: ClamAV using ClamSMTP Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Add dev_pm_qos notifiers to devfreq core in order to support frequency limits via dev_pm_qos_add_request. Unlike the rest of devfreq the dev_pm_qos frequency is measured in kHz, this is consistent with current dev_pm_qos usage for cpufreq and allows frequencies above 2Ghz (pm_qos expresses limits as s32). Like with cpufreq the handling of min_freq/max_freq is moved to the dev_pm_qos mechanism. Constraints from userspace are no longer clamped on store, instead all values can be written and we only check against OPPs in a new devfreq_get_freq_range function. This is consistent with the design of dev_pm_qos. Notifiers from pm_qos are executed under a single global dev_pm_qos_mtx and need to take devfreq->lock, this means that calls into dev_pm_qos while holding devfreq->lock are not allowed (lockdep warns about possible deadlocks). Fix this by only adding the qos request and notifiers after devfreq->lock is released inside devfreq_add_device. In theory this means sysfs writes are possible before the min/max requests are initialized so we guard against that explictly. The dev_pm_qos_update_request function would otherwise print a big WARN splat. Alternatively devfreq initialization could be refactored to avoid taking devfreq->lock but that requires several intricate changes: https://patchwork.kernel.org/cover/11242865/ I considered making dev_pm_qos call notifiers outside the lock but that's another complex refactoring and it's difficult to ensure correctness. If two identical qos requests are made in parallel then the second shouldn't return until all notifiers are completely executed for the first and QOS is enforced; otherwise it mostly defeats the purpose of making proactive requests. This series implements the minimal changes in order to implement dev_pm_qos support for devfreq. It only costs a little defensive programming. This series is also marked as [RFC] because it depends on restoring DEV_PM_QOS_MIN/MAX_FREQUENCY inside the pm core: https://patchwork.kernel.org/cover/11250413/ --- Changes since "big version" v10: * Drop accepted cleanups * Work with current locking approach (split cleanups into other series) * Drop acks and deliberately relabel as a new series. It still incorporates most previous discussion but takes a different approach to locking. * Don't print errors if devfreq_dev_release is called on error cleanup from devfreq_add_device, just accept that requests and notifiers might not be registered yet. I wish dev_pm_qos cleanups behaved like standard "kfree" and silently did nothing when there's nothing to be done. Link to v10: https://patchwork.kernel.org/project/linux-arm-kernel/list/?series=196443 Leonard Crestez (2): PM / devfreq: Add PM QoS support PM / devfreq: Use PM QoS for sysfs min/max_freq drivers/devfreq/devfreq.c | 151 ++++++++++++++++++++++++++++++++++---- include/linux/devfreq.h | 14 +++- 2 files changed, 145 insertions(+), 20 deletions(-)