From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1519120628; cv=none; d=google.com; s=arc-20160816; b=OJ1wxMyqUNj0hnZDr4NScmH3VXf8y7e8wFncd6c7QJzXysweuqEz5VXYtotL3xpXY7 B+YjtE4g1KbSTQ8STqCeKQy8bQXWcb4BtYA8/jU6o7JJQ+dx/SD/tTA34dHvwWyiR7DZ wywBsp/HYpG2foS1JCfFkQqh/5kBMYlZQBwQO6/IvuWlTCeYDuVg1fkWhn0RLttsBblN pAVRIO8cDnBYiMen+mPYjQ/CbT/eQB9zKSTKt6PjQb1k+CRZ1JRJZVe7T/2I6ynBaJH6 3XZNtzjhlcjDOFApe0wvu2Lo7AbrcKtX1DnmUyn/oSQeRHzbA001f/fyJmHBm55AI69n xYYw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=cc:to:subject:message-id:date:from:references:in-reply-to:sender :mime-version:dkim-signature:arc-authentication-results; bh=AJ1isu7Dhg7VTybvrfS6VLDa6Vy4KFB2TmS61XOrsqo=; b=op+Km3cKVRcsafX2UcOzPwFwkLQ2lnXGtFhTyy/2Lx8IL0Bw3CFRvXu9WXrWYfVon1 F3lPnXYF7CYd9Rw6NLprtyx8m69J2uL+YkrK7aeH21bzOcq5i34La3P9tvJ1N+BIy7QM gbzcpjzRMkSAfnAzRqPmH3DHafcfULZjbas9YMQqpUHDMv04JEXJVEDL4wRwkUOdy2zy cP5Fk69OkV+ezdBrLMSLLpk4YB2U7S4nvSwJcxBi3hSdiLk9YRbPuUW8c431V0HvDQ88 tcuLeBfx6CEDiEHRj694wUx8SpVnOqdextB3Er0S9lueMKX+VLLmtuEBGnpIJGHsng2G ZvLQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=gFiRZtJg; spf=pass (google.com: domain of rjwysocki@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=rjwysocki@gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=gFiRZtJg; spf=pass (google.com: domain of rjwysocki@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=rjwysocki@gmail.com X-Google-Smtp-Source: AH8x225sJnTWK+5b6z7r0lht8yrL0t9YejyZWty1hG3fvuw6oK1JOP4364cizP6wX2zZ+ToeLuT+62aed7XPeohnFJo= MIME-Version: 1.0 Sender: rjwysocki@gmail.com In-Reply-To: References: <151908155159.37696.9710083237704994886.stgit@bhelgaas-glaptop.roam.corp.google.com> <151908204614.37696.12828004282495415825.stgit@bhelgaas-glaptop.roam.corp.google.com> From: "Rafael J. Wysocki" Date: Tue, 20 Feb 2018 10:57:07 +0100 X-Google-Sender-Auth: Xkn_xF595vSKc4L1nqa3ANyrv6A Message-ID: Subject: Re: [PATCH v1 2/2] PCI: Allow user to request power management of conventional and hotplug bridges To: Bjorn Helgaas Cc: Linux PCI , Valdis Kletnieks , Mathias Nyman , Linux PM , Mika Westerberg , "Rafael J. Wysocki" , Linux Kernel Mailing List , Lukas Wunner , Peter Wu , Qipeng Zha , Greg Kroah-Hartman , Andreas Noever , Dave Airlie , Qi Zheng Content-Type: text/plain; charset="UTF-8" X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1592872976935903628?= X-GMAIL-MSGID: =?utf-8?q?1592913431607134594?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, Feb 20, 2018 at 10:41 AM, Rafael J. Wysocki wrote: > On Tue, Feb 20, 2018 at 12:14 AM, Bjorn Helgaas wrote: >> From: Bjorn Helgaas >> >> Previously "pcie_port_pm=force" enabled power management of PCI bridges, >> but only for PCIe ports (not conventional PCI bridges) and only for ports >> that do not support hotplug. Those limitations are there because we're not >> confident that all those configurations work, not because the spec requires >> them. >> >> Change "pcie_port_pm=force" to enable power management of conventional PCI >> bridges and hotplug bridges as well as PCIe ports. As with the previous >> PCIe port-only behavior, this is not expected to work in all systems. >> >> Add a "pci=bridge_pm" parameter to reflect the increased scope. For >> backward compatibility, retain "pcie_port_pm=force" as an undocumented >> equivalent. >> >> Add "pci=no_bridge_pm" as an equivalent to "pcie_port_pm=off". This >> disables power management for all PCI bridges, which is results in the same >> behavior as before, since we always disabled power management of >> conventional PCI bridges, and "pcie_port_pm=off" disabled it for PCIe >> ports. >> >> Signed-off-by: Bjorn Helgaas > > Honestly, I wouldn't do that, at least not this way. > > Somebody might be using pcie_port_pm=force already, for example, and > it works for them for PCIe, but the PCI-to-PCI part of the same system > may not. > > IMO the behavior of pcie_port_pm= should be as is and I don't see > what's wrong with it being documented. That said it may be useful to add something like this to the documentation of it in kernel-parameters.txt: [PCIe port power management is needed to enable SoC-wide power management on some SoCs shipping since 2015, so it is enabled by default on systems from 2015 and newer. Some older systems may still benefit from it and it may not work on some newer systems due to hardware problems. Use this parameter in those cases.]