Date: Thu, 10 Nov 2016 11:22:24 +0000
From: Mark Rutland <mark.rutland@arm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "zhichang.yuan" <yuanzhichang@hisilicon.com>, catalin.marinas@arm.com,
        will.deacon@arm.com, robh+dt@kernel.org, bhelgaas@google.com,
        olof@lixom.net, arnd@arndb.de, linux-arm-kernel@lists.infradead.org,
        lorenzo.pieralisi@arm.com, linux-kernel@vger.kernel.org,
        linuxarm@huawei.com, devicetree@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-serial@vger.kernel.org,
        minyard@acm.org, liviu.dudau@arm.com, zourongrong@gmail.com,
        john.garry@huawei.com, gabriele.paoloni@huawei.com,
        zhichang.yuan02@gmail.com, kantyzc@163.com, xuwei5@hisilicon.com,
        marc.zyngier@arm.com
Subject: Re: [PATCH V5 1/3] ARM64 LPC: Indirect ISA port IO introduced
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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.