Re: [PATCH] arm64: PCI: Add quirk for platforms running Windows

Bjorn Helgaas
2023-03-09T17:38:51Z

On Thu, Mar 09, 2023 at 10:52:13AM +0800, Shawn Guo wrote:
> + linux-arm-msm and MSM maintainer Bjorn
>
> On Wed, Mar 08, 2023 at 12:53:10PM -0600, Bjorn Helgaas wrote:
> > On Mon, Feb 27, 2023 at 10:12:21AM +0800, Shawn Guo wrote:
> > > Commit 8fd4391ee717 ("arm64: PCI: Exclude ACPI "consumer" resources from
> > > host bridge windows") introduced a check to remove host bridge register
> > > resources for all arm64 platforms, with the assumption that the PNP0A03
> > > _CRS resources would always be host bridge registers and never as windows
> > > on arm64.
> > >
> > > The assumption stands true until Qualcomm Snapdragon Windows laptops
> > > emerge. These laptops describe host bridge windows in PNP0A03 _CRS
> > > resources instead. For example, the Microsoft Surface Pro X has host
> > > bridges defined as
> > >
> > > Name (_HID, EisaId ("PNP0A08") /* PCI Express Bus */) // _HID: Hardware ID
> > > Name (_CID, EisaId ("PNP0A03") /* PCI Bus */) // _CID: Compatible ID
> > >
> > > Method (_CRS, 0, NotSerialized) // _CRS: Current Resource Settings
> > > {
> > > Name (RBUF, ResourceTemplate ()
> > > {
> > > Memory32Fixed (ReadWrite,
> > > 0x60200000, // Address Base
> > > 0x01DF0000, // Address Length
> > > )
> > > WordBusNumber (ResourceProducer, MinFixed, MaxFixed, PosDecode,
> > > 0x0000, // Granularity
> > > 0x0000, // Range Minimum
> > > 0x0001, // Range Maximum
> > > 0x0000, // Translation Offset
> > > 0x0002, // Length
> > > ,, )
> > > })
> > > Return (RBUF) /* \_SB_.PCI0._CRS.RBUF */
> > > }
> > >
> > > The Memory32Fixed holds a host bridge window, but it's not properly
> > > defined as a "producer" resource. Consequently the resource gets
> > > removed by kernel, and the BAR allocation fails later on:
> > >
> > > [ 0.150731] pci 0002:00:00.0: BAR 14: no space for [mem size 0x00100000]
> > > [ 0.150744] pci 0002:00:00.0: BAR 14: failed to assign [mem size 0x00100000]
> > > [ 0.150758] pci 0002:01:00.0: BAR 0: no space for [mem size 0x00004000 64bit]
> > > [ 0.150769] pci 0002:01:00.0: BAR 0: failed to assign [mem size 0x00004000 64bit]
> > >
> > > This eventually prevents the PCIe NVME drive from being accessible.
> > >
> > > Add a quirk for these platforms to avoid the resource being removed.
> > >
> > > Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
> > > ---
> > > We are running into the issue on more devices than just Surface Pro X
> > > now, so trying to sort it out with a quirk as suggested by Lorenzo [1].
> >
> > One thing I don't like about this application of quirks is that the
> > list of affected platforms is likely to grow, which is an ongoing
> > burden for users and developers.
>
> It's a very reasonable concern. I really hope that Qualcomm will start
> thinking about Linux support on these machines in the future not too far
> away, so that the list will not grow too long.
>
> > Can we have a conversation with Qualcomm about how they *intend* this
> > to work? Linux is probably doing something wrong (interpreting
> > something differently than Windows does), and if we could fix that, we
> > have a better chance of future platforms working without quirks.
>
> Today Qualcomm only ships and cares about Windows on these machines, but
> I believe it will change sooner or later.

I don't maintain arch/arm64/kernel/pci.c, but my opinion is that we
should not pursue quirks like this until we've tried really hard to
figure out a generic approach.

Bjorn