linux-kernel - Re: [PATCH 12/12] PM / core: Add AVOID

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Message-ID: <2493317.bKYzDQ0iOo@aspire.rjw.lan>
Date:   Tue, 17 Oct 2017 17:59:23 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Documentation <linux-doc@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Kevin Hilman <khilman@...nel.org>,
        Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 12/12] PM / core: Add AVOID_RPM driver flag

On Tuesday, October 17, 2017 5:33:17 PM CEST Andy Shevchenko wrote:
> On Mon, 2017-10-16 at 03:32 +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > Define and document a new driver flag, DPM_FLAG_AVOID_RPM, to inform
> > the PM core and middle layer code that the driver has something
> > significant to do in its ->suspend and/or ->resume callbacks and
> > runtime PM should be disabled for the device when these callbacks
> > run.
> > 
> > Setting DPM_FLAG_AVOID_RPM (in addition to DPM_FLAG_SMART_SUSPEND)
> > causes runtime PM to be disabled for the device before invoking the
> > driver's ->suspend callback for it and to be enabled again for it
> > only after the driver's ->resume callback has returned.  In addition
> > to that, if the device is in runtime suspend right after disabling
> > runtime PM for it (which means that there was no reason to resume it
> > from runtime suspend beforehand), the invocation of the ->suspend
> > callback will be skipped for it and it will be left in runtime
> > suspend until the "noirq" phase of the subsequent system resume.
> > 
> > If DPM_FLAG_SMART_SUSPEND is not set, DPM_FLAG_AVOID_RPM has no
> > effect.
> > 
> 
> > +	if (dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) &&
> > +	    dev_pm_test_driver_flags(dev, DPM_FLAG_AVOID_RPM)) {
> 
> Wasn't interface designed to allow something like:
> 	if (dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND | DPM_FLAG_AVOID_RPM)) {
> instead?

That would return true if any of them was set and both are needed here.

> Does it make sense to have a separate definition for
> DPM_FLAG_SMART_SUSPEND | DPM_FLAG_AVOID_RPM ?

Yes, it does IMO, because if you don't provide ->suspend and ->resume
callbacks, it is sufficient if runtime PM is disabled for the device
in __device_suspend_late() which happens anyway.

DPM_FLAG_AVOID_RPM is about disabling it earlier.

Thanks,
Rafael