Date:   Fri, 2 Sep 2016 11:25:27 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Chen Yu <yu.c.chen@...el.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH][RFC v3] PCI: Workaround to enable poweroff on Mac Pro 11

On Wed, Aug 24, 2016 at 04:17:31PM +0200, Lukas Wunner wrote:
> On Fri, Aug 19, 2016 at 04:30:25PM +0800, Chen Yu wrote:
> > People reported that they can not do a poweroff nor a
> > suspend to ram on their Mac Pro 11. After some investigations
> > it was found that, once the PCI bridge 0000:00:1c.0 reassigns its
> > mm windows to ([mem 0x7fa00000-0x7fbfffff] and
> > [mem 0x7fc00000-0x7fdfffff 64bit pref]), the region of ACPI
> > io resource 0x1804 becomes unaccessible immediately, where the
> > ACPI Sleep register is located, as a result neither poweroff(S5)
> > nor suspend to ram(S3) works.
> 
> To provide a bit more context:
> 
> The root port in question (0000:00:1c.0) is not listed in the DSDT.
> On macOS, only devices present in the ACPI namespace are incorporated
> into the I/O Kit registry. Consequently macOS pretends that this root
> port doesn't exist. It's not listed in the "ioreg -l" output and thus
> no driver is attached to this device.
> 
> So what we're dealing with is sloppiness on the part of Apple:
> Some engineer probably forgot to disable this unused root port
> and they didn't notice it during testing because their OS ignores
> such devices.
> 
> We could in principle achieve the same behaviour by adding a PCI
> device only if it has an ACPI companion, perhaps quirk this only
> to Macs. I'm not sure if that's the right thing to do though.
> What if they hide devices from macOS but we want to access them
> on Linux?
> 
> What's really odd is that changing *memory* windows affects
> accessibility of *I/O ports*.
> 
> One theory would be that I/O ports are somehow mapped into memory.
> The GPIO pins of Intel chipsets are usually accessible through
> I/O ports, but I've recently looked at the DSDT of the newest
> MacBook9,1 (2016) and it looks like they're now accessed through
> SystemMemory instead of SystemIO. Perhaps someone at Intel knows
> about these intricacies of their chipsets.

Hey, look, Chen Yu works at Intel :)

This apparent connection between memory windows and I/O port
accessibility is indeed very concerning.

I know there are PCI host bridges with windows that translate CPU
memory accesses into PCI I/O port accesses.  If this is one of them,
and it has such a window enabled at the address we happened to choose
for the mem window, that would be a problem.

I assume this would be documented somewhere in the chipset datasheet.

> If I/O ports are indeed mapped into memory, we need to find a way
> to identify and reserve that region. So while this patch seems
> like a workable and sufficiently small fix, it might mask a larger
> underlying issue. It's certainly a problem though that these
> machines currently cannot power off or suspend.
> 
> FWIW, we have a somewhat similar issue with the Apple gmux
> (a microcontroller built into dual GPU MacBook Pros). That chip
> is attached to the LPC bus and accessed through I/O ports.
> It turns out that once VGA IO is locked to the discrete GPU
> using vgaarb, gmux' I/O ports suddenly become inaccessible.
> Apparently its I/O ports are routed to the secondary PCI bus
> to which the discrete GPU is connected, and no longer to the
> root bus on which the LPC bridge resides. However gmux' I/O ports
> are in the 0x700-0x7ff range, whereas the VGA registers are in
> the 0x3b0-0x3bb and 0x3c0-0x3df range. So that's another oddity
> of Intel chipsets with regards to I/O accessibility.
> 
> Best regards,
> 
> Lukas
> 
> > 
> > As suggested by Bjorn, further testing shows that, there is an
> > unreported device may be (using) conflict with above aperture,
> > which brings unpredictable result such as the failure of accessing
> > the io port, which blocks the poweroff(S5). Besides if we reassign
> > the memory aperture to the other place, the poweroff works again.
> > 
> > As we do not find any resource declared in _CRS which contain above
> > memory aperture, and Mac OS does not use this pci bridge neither, we
> > choose a simple workaround to clear the hotplug flag(suggested by
> > Yinghai Lu), thus do not allocate any resource for this pci bridge,
> > and thereby no conflict anymore.
> > 
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=103211
> > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > Cc: Rafael J. Wysocki <rafael@...nel.org>
> > Cc: Lukas Wunner <lukas@...ner.de>
> > Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> > ---
> >  drivers/pci/quirks.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 37ff015..04bbdba 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -2776,6 +2776,26 @@ static void quirk_hotplug_bridge(struct pci_dev *dev)
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_HINT, 0x0020, quirk_hotplug_bridge);
> >  
> >  /*
> > + * Apple: Avoid programming the memory/io aperture of 00:1c.0
> > + *
> > + * BIOS does not declare any resource for 00:1c.0, but with
> > + * hotplug flag set, thus the OS allocates:
> > + * [mem 0x7fa00000 - 0x7fbfffff]
> > + * [mem 0x7fc00000-0x7fdfffff 64bit pref]
> > + * which is conflict with an unreported device, which
> > + * causes unpredictable result such as accessing io port.
> > + * So clear the hotplug flag to work around it.
> > + */
> > +static void quirk_apple_mbp_poweroff(struct pci_dev *dev)
> > +{
> > +	if (dmi_match(DMI_PRODUCT_NAME, "MacBookPro11,4") ||
> > +	    dmi_match(DMI_PRODUCT_NAME, "MacBookPro11,5"))
> > +		dev->is_hotplug_bridge = 0;
> > +}
> > +
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x8c10, quirk_apple_mbp_poweroff);
> > +
> > +/*
> >   * This is a quirk for the Ricoh MMC controller found as a part of
> >   * some mulifunction chips.
> >  
> > -- 
> > 2.7.4
> > 
> --
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