linux-kernel - Re: Time to re-enable Runtime PM per default for PCI devcies?

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Date:   Tue, 17 Nov 2020 10:38:17 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Kai Heng Feng <kai.heng.feng@...onical.com>,
        Lukas Wunner <lukas@...ner.de>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Time to re-enable Runtime PM per default for PCI devcies?

[+to Rafael, author of the commit you mentioned,
+cc Mika, Kai Heng, Lukas, linux-pm, linux-kernel]

On Tue, Nov 17, 2020 at 04:56:09PM +0100, Heiner Kallweit wrote:
> More than 10 yrs ago Runtime PM was disabled per default by bb910a7040
> ("PCI/PM Runtime: Make runtime PM of PCI devices inactive by default").
> 
> Reason given: "avoid breakage on systems where ACPI-based wake-up is
> known to fail for some devices"
> Unfortunately the commit message doesn't mention any affected  devices
> or systems.
> 
> With Runtime PM disabled e.g. the PHY on network devices may remain
> powered up even with no cable plugged in, affecting battery lifetime
> on mobile devices. Currently we have to rely on the respective distro
> or user to enable Runtime PM via sysfs (echo auto > power/control).
> Some devices work around this restriction by calling pm_runtime_allow
> in their probe routine, even though that's not recommended by
> https://www.kernel.org/doc/Documentation/power/pci.txt
> 
> Disabling Runtime PM per default seems to be a big hammer, a quirk
> for affected devices / systems may had been better. And we still
> have the option to disable Runtime PM for selected devices via sysfs.
> 
> So, to cut a long story short: Wouldn't it be time to remove this
> restriction?

I don't know the history of this, but maybe Rafael or the others can
shed some light on it.