linux-kernel - Re: [PATCH v8 2/2] PCI/ACPI: Use device constraints instead of dates to opt devices into D3

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Date:   Fri, 4 Aug 2023 09:07:43 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Iain Lane <iain@...ngesquash.org.uk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v8 2/2] PCI/ACPI: Use device constraints instead of dates
 to opt devices into D3

On Thu, Aug 03, 2023 at 10:18:07AM -0500, Mario Limonciello wrote:
> On 8/3/2023 10:14, Mika Westerberg wrote:
> > On Thu, Aug 03, 2023 at 06:38:45AM -0500, Mario Limonciello wrote:
> > > On 8/3/23 00:01, Mika Westerberg wrote:
> > > > Hi,
> > > > 
> > > > On Wed, Aug 02, 2023 at 03:10:13PM -0500, Mario Limonciello wrote:
> > > > > @@ -3036,11 +3044,8 @@ bool pci_bridge_d3_possible(struct pci_dev *bridge)
> > > > >    		if (dmi_check_system(bridge_d3_blacklist))
> > > > >    			return false;
> > > > > -		/*
> > > > > -		 * It should be safe to put PCIe ports from 2015 or newer
> > > > > -		 * to D3.
> > > > > -		 */
> > > > > -		if (dmi_get_bios_year() >= 2015)
> > > > > +		/* the platform indicates in a device constraint that D3 is needed */
> > > > > +		if (platform_constraint_d3(bridge))
> > > > 
> > > > This for sure causes some sort of power regression on the Intel
> > > > platforms made after 2015. Why not check for the constraint and:
> > > > 
> > > Are you sure?  I saw it as an explanation of how Windows could put the
> > > systems into D3 when there is no other PM related ACPI objects.
> > 
> > I'm concerned if there are no PEP constraints on some of the affected
> > systems this now leaves root ports into D0 then, no?
> 
> Do you have any idea if any of the affected systems were something that
> didn't ship with Windows?  Like an Apple system or a Chromebook?

Some of them, at least the Apollo Lake ones were used in IVI systems
that did not run Windows IIRC.

> If so; I'd think it's better to treat those as "quirks" rather than make a
> blanket policy from the timing.

It is possible that the quirk list ends up being rather big (or not) so
it may be considered something that is painful to maintain.