[PATCH] acpi: pci: don't ignore function ID of bridge device in _PRT

[Ard Biesheuvel]

On 7 April 2017 at 18:06, Bjorn Helgaas <helgaas at kernel.org> wrote:
> Hi Ard,
>
> On Fri, Apr 07, 2017 at 02:22:22PM +0100, Ard Biesheuvel wrote:
>> We currently derive legacy interrupt routing by matching _PRT
>> entries on the PCI device only, presumably under the assumption
>> that PRT entries always have a value of 0xffff in the function
>> field, meaning 'match all functions'.
>
> The spec (ACPI v6.0, sec 6.2.13) contains a note that:
>
>   The PCI function number in the Address field of the _PRT packages
>   must be 0xFFFF, indicating "any" function number or "all functions".
>
> If we need a patch like this, we need to somehow reconcile it with
> that spec text to make sure firmware and OS folks have a common
> understanding of how this is supposed to work.
>
>> This no longer holds for modern PCIe topologies, where the
>> legacy interrupts for different slots may be wired to different
>> functions on the same bridge device. For instance, on AMD Seattle,
>> we may have something like
>>
>> -[0000:00]-+-00.0  Advanced Micro Devices, Inc. [AMD] Device 1a00
>>            +-02.0  Advanced Micro Devices, Inc. [AMD] Device 1a01
>>            +-02.2-[01]----00.0  Renesas uPD720202 USB 3.0 Host Controller
>>            \-02.3-[02]----00.0  Realtek RTL8169 PCIe Gigabit Ethernet
>>
>> where the _PRT describes the legacy interrupt routing as
>>
>>     Name (_PRT, Package ()  // _PRT: PCI Routing Table
>>     {
>>         // slot 1: dev 2 fn 1
>>         Package () { 0x20001, 0x0, 0x0, 0x140 },
>>         Package () { 0x20001, 0x1, 0x0, 0x141 },
>>         Package () { 0x20001, 0x2, 0x0, 0x142 },
>>         Package () { 0x20001, 0x3, 0x0, 0x143 },
>>
>>         // slot 1: dev 2 fn 2
>>         Package () { 0x20002, 0x0, 0x0, 0x144 },
>>         Package () { 0x20002, 0x1, 0x0, 0x145 },
>>         Package () { 0x20002, 0x2, 0x0, 0x146 },
>>         Package () { 0x20002, 0x3, 0x0, 0x147 },
>>
>>         // slot 1: dev 2 fn 3
>>         Package () { 0x20003, 0x0, 0x0, 0x148 },
>>         Package () { 0x20003, 0x1, 0x0, 0x149 },
>>         Package () { 0x20003, 0x2, 0x0, 0x14a },
>>         Package () { 0x20003, 0x3, 0x0, 0x14b }
>>     }) // _PRT
>
> But I think this _PRT description is incorrect and we should change
> the _PRT rather than the kernel.  My laptop has a basically identical
> topology:
>
>   -[0000:00]-+-00.0  Intel Corporation Sky Lake Host Bridge/DRAM Registers
>              +-1c.0-[02]----00.0  Realtek Semiconductor Co., Ltd.  Device 525a
>              +-1c.2-[04]----00.0  Intel Corporation Wireless 8260
>
> and the ASL looks like this (paraphrased):
>
>   Device (EXP1) {
>     Name (_ADR, 0x001C0000)
>     Name (_PRT) {
>       Package () { 0xFFFF, 0x00, \_SB.LNKA, 0x00 },
>       Package () { 0xFFFF, 0x01, \_SB.LNKB, 0x00 },
>       ...
>     }
>   }
>   Device (EXP3) {
>     Name (_ADR, 0x001C0002)
>     Name (_PRT) {
>       Package () { 0xFFFF, 0x00, \_SB.LNKC, 0x00 },
>       Package () { 0xFFFF, 0x01, \_SB.LNKD, 0x00 },
>       ...
>     }
>   }
>

Thanks for the explanation. But how is this wired up into the PNP0A08
device then? IOW, how does the ACPI code in Linux discover the
relation between these devices and my PCI root device?