linux-kernel - Re: [PATCH V5 1/3] ARM64 LPC: Indirect ISA port IO introduced

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Message-ID: <20161110112224.GB4418@leverpostej>
Date:   Thu, 10 Nov 2016 11:22:24 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     "zhichang.yuan" <yuanzhichang@...ilicon.com>,
        catalin.marinas@....com, will.deacon@....com, robh+dt@...nel.org,
        bhelgaas@...gle.com, olof@...om.net, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, lorenzo.pieralisi@....com,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com,
        devicetree@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-serial@...r.kernel.org, minyard@....org, liviu.dudau@....com,
        zourongrong@...il.com, john.garry@...wei.com,
        gabriele.paoloni@...wei.com, zhichang.yuan02@...il.com,
        kantyzc@....com, xuwei5@...ilicon.com, marc.zyngier@....com
Subject: Re: [PATCH V5 1/3] ARM64 LPC: Indirect ISA port IO introduced

On Wed, Nov 09, 2016 at 10:16:42AM +1100, Benjamin Herrenschmidt wrote:
> On Tue, 2016-11-08 at 12:03 +0000, Mark Rutland wrote:
> > On Tue, Nov 08, 2016 at 11:47:07AM +0800, zhichang.yuan wrote:
> > > 
> > > For arm64, there is no I/O space as other architectural platforms, such as
> > > X86. Most I/O accesses are achieved based on MMIO. But for some arm64 SoCs,
> > > such as Hip06, when accessing some legacy ISA devices connected to LPC, those
> > > known port addresses are used to control the corresponding target devices, for
> > > example, 0x2f8 is for UART, 0xe4 is for ipmi-bt. It is different from the
> > > normal MMIO mode in using.
> > 
> > This has nothing to do with arm64. Hardware with this kind of indirect
> > bus access could be integrated with a variety of CPU architectures. It
> > simply hasn't been, yet.
> 
> On some ppc's we also use similar indirect access methods for IOs. We
> have a generic infrastructure for re-routing some memory or IO regions
> to hooks.
> 
> On POWER8, our PCIe doesn't do IO at all, but we have an LPC bus behind
> firmware calls ;-) We use that infrastructure to plumb in the LPC bus.

Just to check, do you hook that in your inb/outb/etc?

Generally, it would seem nicer if we could have higher-level
isa_{inb,outb,whatever} accessors that we could hook separately from
other IO.

We don't necessarily have to move all ISA drivers over to that if we had
a separate symbol for that interface.

Thanks,
Mark.