linux-kernel - Re: [PATCH] PCI / PM: Extend PME polling to all PCI devices

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Date:	Fri, 14 Oct 2011 09:08:10 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Mailing List <linux-acpi@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI / PM: Extend PME polling to all PCI devices

On Mon, 3 Oct 2011 23:16:33 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> The land of PCI power management is a land of sorrow and ugliness,
> especially in the area of signaling events by devices.  There are
> devices that set their PME Status bits, but don't really bother
> to send a PME message or assert PME#.  There are hardware vendors
> who don't connect PME# lines to the system core logic (they know
> who they are).  There are PCI Express Root Ports that don't bother
> to trigger interrupts when they receive PME messages from the devices
> below.  There are ACPI BIOSes that forget to provide _PRW methods for
> devices capable of signaling wakeup.  Finally, there are BIOSes that
> do provide _PRW methods for such devices, but then don't bother to
> call Notify() for those devices from the corresponding _Lxx/_Exx
> GPE-handling methods.  In all of these cases the kernel doesn't have
> a chance to receive a proper notification that it should wake up a
> device, so devices stay in low-power states forever.  Worse yet, in
> some cases they continuously send PME Messages that are silently
> ignored, because the kernel simply doesn't know that it should clear
> the device's PME Status bit.
> 
> This problem was first observed for "parallel" (non-Express) PCI
> devices on add-on cards and Matthew Garrett addressed it by adding
> code that polls PME Status bits of such devices, if they are enabled
> to signal PME, to the kernel.  Recently, however, it has turned out
> that PCI Express devices are also affected by this issue and that it
> is not limited to add-on devices, so it seems necessary to extend
> the PME polling to all PCI devices, including PCI Express and planar
> ones.  Still, it would be wasteful to poll the PME Status bits of
> devices that are known to receive proper PME notifications, so make
> the kernel (1) poll the PME Status bits of all PCI and PCIe devices
> enabled to signal PME and (2) disable the PME Status polling for
> devices for which correct PME notifications are received.
> 
> Tested-by: Sarah Sharp <sarah.a.sharp@...ux.intel.com>
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> ---

Applied to linux-next, thanks.

-- 
Jesse Barnes, Intel Open Source Technology Center

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