From: Arnd Bergmann <arnd@arndb.de>
To: linux-arm-kernel@lists.infradead.org
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Mark Rutland <mark.rutland@arm.com>, gabriele.paoloni@huawei.com,
        benh@kernel.crashing.org, will.deacon@arm.com, linuxarm@huawei.com,
        lorenzo.pieralisi@arm.com, xuwei5@hisilicon.com,
        linux-serial@vger.kernel.org, catalin.marinas@arm.com,
        devicetree@vger.kernel.org, minyard@acm.org, marc.zyngier@arm.com,
        liviu.dudau@arm.com, john.garry@huawei.com, zourongrong@gmail.com,
        robh+dt@kernel.org, bhelgaas@google.com, kantyzc@163.com,
        zhichang.yuan02@gmail.com, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        "zhichang.yuan" <yuanzhichang@hisilicon.com>, olof@lixom.net
Subject: Re: [PATCH V5 2/3] ARM64 LPC: Add missing range exception for special ISA
Date: Fri, 18 Nov 2016 10:22:46 +0100
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On Monday, November 14, 2016 11:11:11 AM CET One Thousand Gnomes wrote:
> > > It's not a safe assumption for x86 at least. There are a few systems with
> > > multiple ISA busses particularly older laptops with a docking station.  
> > 
> > But do they have multiple ISA domains? There is no real harm in supporting
> > it, the (small) downsides I can think of are:
> 
> I don't believe they x86 class ones have multiple ISA domains. But as
> I've said I don't know how the electronics in the older ThinkPad worked
> when it used two PIIX4s with some LPC or ISA stuff on each.
> 
> It works in DOS and unmodified Linux so I'm pretty sure there are no
> additional domains. Likewise the various x86 schemes that route some bits
> of ISA bus off into strange places work in DOS and don't have any
> overlaps.
> 
> yenta_socket handles PCI/PCMCIA bridging and routes a range of that flat
> ISA space appropriately to the card.

Right, that's what I had expected, so we still don't even
need to handle multiple ISA I/O address spaces for the
only known case of multiple ISA buses, though we may decide
to generalize the code like that anyway.

	Arnd