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Subject: Re: [PATCH v3 2/2] asm-generic: Add new pci.h and use it
From:   Jessica Clarke <jrtc27@jrtc27.com>
In-Reply-To: <CAK8P3a2aTS74TG8F+cVHX969hMQHKP3Ai5V0h-m+GeAq6kq5pQ@mail.gmail.com>
Date:   Fri, 22 Jul 2022 22:39:18 +0100
Cc:     Rob Herring <robh@kernel.org>, Palmer Dabbelt <palmer@dabbelt.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Maciej W. Rozycki" <macro@orcam.me.uk>,
        Stafford Horne <shorne@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Guo Ren <guoren@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        linux-csky@vger.kernel.org,
        linux-riscv <linux-riscv@lists.infradead.org>,
        linux-um <linux-um@lists.infradead.org>,
        PCI <linux-pci@vger.kernel.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@vger.kernel.org>
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To:     Arnd Bergmann <arnd@arndb.de>
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On 22 Jul 2022, at 20:55, Arnd Bergmann <arnd@arndb.de> wrote:
>=20
> On Fri, Jul 22, 2022 at 6:36 PM Rob Herring <robh@kernel.org> wrote:
>> On Fri, Jul 22, 2022 at 9:27 AM Palmer Dabbelt <palmer@dabbelt.com> =
wrote:
>>=20
>> =46rom fu740:
>>                       ranges =3D <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?
>=20
> The PCI-side port number 0x60080000 gets turned into Linux I/O =
resource 0,
> which I think is what __pci_assign_resource operates on.
>=20
> 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?
>=20
> 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.

Possibly related is the (harmless) warning spew seen during boot on
FreeBSD. The bridge, and all downstream ones, reset to having I/O
window 0x0-0xfff and memory/prefetch window 0x0-0xfffff (which FreeBSD
tries to allocate, fails because that=E2=80=99s outside the valid ranges =
above,
so it then just paves over with a sane fresh config). Linux resets the
controller on probe so this is the initial state when enumerating, and
perhaps that=E2=80=99s not handled so gracefully as on FreeBSD (which =
also
resets in device_attach, the second half of what Linux calls probe)?

Jess