Date:   Fri, 10 Mar 2023 14:26:55 +0100
From:   Lorenzo Pieralisi <lpieralisi@kernel.org>
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Shawn Guo <shawn.guo@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Maximilian Luz <luzmaximilian@gmail.com>,
        linux-pci@vger.kernel.org, linux-acpi@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: PCI: Add quirk for platforms running Windows
Message-ID: <ZAswHyaYjeqjW/+A@lpieralisi>
References: <20230227021221.17980-1-shawn.guo@linaro.org>
 <20230308185310.GA1030878@bhelgaas>
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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.
> 
> 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.

Catch-22. What if some firmware would add host bridge MMIO register
space (marked as consumer) in the _CRS ? We would end up allocating
BAR regions in there, which is not right, so your commit:

8fd4391ee717 ("arm64: PCI: Exclude ACPI "consumer" resources from host bridge windows")

is correct and if we revert it we would trigger regressions on some
arm64 platforms for the reason I mention above.

We can look for clarification at ACPI specs level but for firmware
that is out there I am not sure what options we have.

Lorenzo

> > [1] https://lore.kernel.org/all/20210527093200.GA16444@lpieralisi/
> > 
> >  arch/arm64/kernel/pci.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> > 
> > diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> > index 2276689b5411..896dbd028b67 100644
> > --- a/arch/arm64/kernel/pci.c
> > +++ b/arch/arm64/kernel/pci.c
> > @@ -109,16 +109,42 @@ int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
> >  	return 0;
> >  }
> >  
> > +#define QCOM_DSDT_QUIRK "Host bridge windows in PNP0A03 _CRS"
> > +
> > +static struct acpi_platform_list qcom_platlist[] = {
> > +	/* Thinkpad X13s */
> > +	{ "LENOVO", "SDM8280 ", 0, ACPI_SIG_DSDT, all_versions, QCOM_DSDT_QUIRK },
> > +	/* Microsoft Surface Pro 9 (5G) and Windows Dev Kit 2023 */
> > +	{ "QCOMM ", "SDM8280 ", 0, ACPI_SIG_DSDT, all_versions, QCOM_DSDT_QUIRK },
> > +	/* Microsoft Surface Pro X */
> > +	{ "QCOMM ", "SDM8180 ", 0, ACPI_SIG_DSDT, all_versions, QCOM_DSDT_QUIRK },
> > +	{ }
> > +};
> > +
> >  static int pci_acpi_root_prepare_resources(struct acpi_pci_root_info *ci)
> >  {
> >  	struct resource_entry *entry, *tmp;
> >  	int status;
> > +	int idx;
> >  
> >  	status = acpi_pci_probe_root_resources(ci);
> > +
> > +	/*
> > +	 * Most arm64 platforms that do not run Windows describe host bridge
> > +	 * registers in PNP0A03 _CRS resources, but some like Qualcomm
> > +	 * Snapdragon Windows laptops describe host bridge windows in there.
> > +	 * We do not want to destroy the resources for these platforms.
> > +	 */
> > +	idx = acpi_match_platform_list(qcom_platlist);
> > +	if (idx >= 0)
> > +		goto done;
> > +
> >  	resource_list_for_each_entry_safe(entry, tmp, &ci->resources) {
> >  		if (!(entry->res->flags & IORESOURCE_WINDOW))
> >  			resource_list_destroy_entry(entry);
> >  	}
> > +
> > +done:
> >  	return status;
> >  }
> >  
> > -- 
> > 2.17.1
> >