From: Arnd Bergmann <arnd@arndb.de>
To: Tomasz Nowicki <tn@semihalf.com>
Subject: Re: [PATCH V2 00/23] MMCONFIG refactoring and support for ARM64 PCI hostbridge init based on ACPI
Date: Mon, 21 Dec 2015 15:15:54 +0100
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Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>, okaya@codeaurora.org,
        bhelgaas@google.com, will.deacon@arm.com, catalin.marinas@arm.com,
        rjw@rjwysocki.net, hanjun.guo@linaro.org, jiang.liu@linux.intel.com,
        stefano.stabellini@eu.citrix.com, robert.richter@caviumnetworks.com,
        mw@semihalf.com, liviu.dudau@arm.com, ddaney@caviumnetworks.com,
        tglx@linutronix.de, wangyijing@huawei.com,
        suravee.suthikulpanit@amd.com, msalter@redhat.com,
        linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
        linaro-acpi@lists.linaro.org, jchandra@broadcom.com, jcm@redhat.com
References: <1450278993-12664-1-git-send-email-tn@semihalf.com> <20151221121050.GB11145@red-moon> <5677F3C8.8040200@semihalf.com>
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On Monday 21 December 2015, Tomasz Nowicki wrote:
> On 21.12.2015 13:10, Lorenzo Pieralisi wrote:
> > On Fri, Dec 18, 2015 at 06:56:39PM +0000, okaya@codeaurora.org wrote:

> >> I have multiple root ports with the same IO port configuration in the
> >> current ACPI table.
> >>
> >> Root port 0 = IO range 0x1000-0x10FFF
> >> Root port 1 = IO range 0x1000-0x10FFF
> >> Root port 2 = IO range 0x1000-0x10FFF
> >
> > It is fine. You end up mapping for each of those a 4k window of the
> > virtual address space allocated to IO and that's what you will have in
> > the kernel PCI resources (not in the HW BARs though). If that was a problem
> > it would be even for the current DT host controllers eg:
> >
> > arch/arm64/boot/dts/apm/apm-storm.dtsi
> >
> > it should not be (again I will let Arnd comment on this since he may be
> > aware of issues encountered on other arches/platforms).
> >
> 
> Root port 0 = IO range 0x1000-0x10FFF
> Root port 1 = IO range 0x1000-0x10FFF
> Root port 2 = IO range 0x1000-0x10FFF
> 
> If above ranges are mapped into different CPU windows, then yes, it is fine.

Ideally, they should all be the same CPU address so we only have to map the window
once, each device gets an address below 64K, and you can have legacy port numbers
(below 4K) on any bus, which is required to make certain GPUs work.

I haven't actually seen anyone do that on ARM though, every implementation so
far has a separate mapping per host bridge, and we can cope with that too,
and we can live with either overlapping bus addresses or unique bus addresses,
any of them can be expressed by the PCI core in Linux, we just have to make sure
that we correctly translate the firmware tables into our internal structures.

	Arnd
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