Hi, Ben,


On 2016/11/9 7:16, 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.

I am interested on the generic infrastructure on PPC.
Could you point out where those drivers are?
want to take a look..

Thanks,
Zhichang

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.

quoted

quoted

To drive these devices, this patch introduces a method named indirect-IO.
In this method the in/out pair in arch/arm64/include/asm/io.h will be
redefined. When upper layer drivers call in/out with those known legacy port
addresses to access the peripherals, the hooking functions corrresponding to
those target peripherals will be called. Through this way, those upper layer
drivers which depend on in/out can run on Hip06 without any changes.

As above, this has nothing to do with arm64, and as such, should live in
generic code, exactly as we would do if we had higher-level ISA
accessor ops.

Regardless, given the multi-instance case, I don't think this is
sufficient in general (and I think we need higher-level ISA accessors
to handle the indirection).

Multi-instance with IO is tricky to do generically because archs already
have all sort of hacks to deal with the fact that inb/outb don't require
an explicit ioremap, so an IO resource can take all sort of shape depending
on the arch.

Overall it boils down to applying some kind of per-instance "offset" to
the IO port number though.