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:

quoted

On Tue, Nov 08, 2016 at 11:47:07AM +0800, zhichang.yuan wrote:

quoted

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.