linux-kernel - Re: [PATCH v3 2/2] asm-generic: Add new pci.h and use it

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Message-ID: <CAK8P3a2aTS74TG8F+cVHX969hMQHKP3Ai5V0h-m+GeAq6kq5pQ@mail.gmail.com>
Date:   Fri, 22 Jul 2022 21:55:03 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Rob Herring <robh@...nel.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Stafford Horne <shorne@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-csky@...r.kernel.org,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-um <linux-um@...ts.infradead.org>,
        PCI <linux-pci@...r.kernel.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] asm-generic: Add new pci.h and use it

On Fri, Jul 22, 2022 at 6:36 PM Rob Herring <robh@...nel.org> wrote:
> On Fri, Jul 22, 2022 at 9:27 AM Palmer Dabbelt <palmer@...belt.com> wrote:
>
> From fu740:
>                        ranges = <0x81000000  0x0 0x60080000  0x0
> 0x60080000 0x0 0x10000>,      /* I/O */
...
> So again, how does one get a 0 address handed out when that's not even
> a valid region according to DT? Is there some legacy stuff that
> ignores the bridge windows?

The PCI-side port number 0x60080000 gets turned into Linux I/O resource 0,
which I think is what __pci_assign_resource operates on.

The other question is why the platform would want to configure the
PCI bus to have a PCI I/O space window of size 0x10000 at the address
it's mapped into, rather than putting it at address zero. Is this a hardware
bug, a bootloader bug, or just badly set up in the DT?

Putting the PCI address of the I/O space window at port 0 is usually
better because it works with PCI devices and drivers that assume that
port numbers are below 0xfffff, and makes the PCI port number match
the Linux port number.

         Arnd