Re: [PATCH] PCI: Blacklist power management of Gigabyte X299 DESIGNARE EX PCIe ports

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On Tue, Dec 04, 2018 at 06:55:41PM +0100, Rafael J. Wysocki wrote:
> On Tuesday, December 4, 2018 12:20:48 PM CET Mika Westerberg wrote:
> > Gigabyte X299 DESIGNARE EX motherboard has one PCIe root port that is
> > connected to an Alpine Ridge Thunderbolt controller. This port has slot
> > implemented bit set in the config space but other than that it is not
> > hotplug capable in the sense we are expecting in Linux (it has
> > dev->is_hotplug_bridge set to 0):
> > 
> > 00:1c.4 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #5
> >         Bus: primary=00, secondary=05, subordinate=46, sec-latency=0
> >         Memory behind bridge: 78000000-8fffffff [size=384M]
> >         Prefetchable memory behind bridge: 00003800f8000000-00003800ffffffff [size=128M]
> >         ...
> >         Capabilities: [40] Express (v2) Root Port (Slot+), MSI 00
> >         ...
> >                 SltCap: AttnBtn- PwrCtrl- MRL- AttnInd- PwrInd- HotPlug- Surprise-
> >                         Slot #8, PowerLimit 25.000W; Interlock- NoCompl+
> >                 SltCtl: Enable: AttnBtn- PwrFlt- MRL- PresDet- CmdCplt- HPIrq- LinkChg-
> >                         Control: AttnInd Unknown, PwrInd Unknown, Power- Interlock-
> >                 SltSta: Status: AttnBtn- PowerFlt- MRL- CmdCplt- PresDet- Interlock-
> >                         Changed: MRL- PresDet+ LinkState+
> > 
> > This system is using ACPI based hotplug to notify the OS that it needs
> > to rescan the PCI bus (ACPI hotplug).
> > 
> > If there is nothing connected in any of the Thunderbolt ports the root
> > port will not have any runtime PM active children and is thus
> > automatically runtime suspended pretty soon after boot by PCI PM core.
> > Now, when a device is connected the BIOS SMI handler responsible for
> > enumerating newly added devices is not able to find anything because the
> > port is in D3.
> > 
> > Prevent this from happening by blacklisting PCI power management of this
> > particular Gigabyte system.
> > 
> > Reported-by: Kedar A Dongre <kedar.a.dongre@xxxxxxxxx>
> > Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > ---
> > I checked booting Windows on the same system and it does not put any of the
> > PCIe root ports to low power states so there is no issue in Windows. I'm
> > also quite certain Windows does not have similar blacklist.
> 
> Well, that only means that Windows uses a different approach to decide whether
> or not to use PCI PM on PCIe root ports (but we knew that that would be the
> case upfront, didn't we?).

Indeed we did.

> > I wonder if our pci_bridge_d3_possible() heuristics would need to be
> > refined somehow? At least if this blacklist starts growing.
> 
> Because Windows uses a different approach here, there will be systems for
> which Linux will decide to use PCI PM with PCIe root ports and Windows
> won't (or vice versa).  That will cause Linux to use configurations that
> have not been validated against Windows, so it is likely that some of them
> will not work.  Hence, the need for a blacklist is not a surprise really.

Fair enough :)

> So
> 
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Thanks!

> BTW, what version of Windows you have tested?

I only tested Windows 10 1803.



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