Re: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on Hip06

From: Arnd Bergmann
Date: Fri Nov 18 2016 - 06:47:39 EST

[found this old mail in my drafts folder, might as well send it now]

On Thursday, November 10, 2016 8:36:24 PM CET zhichang.yuan wrote:
> Sorry! I can't catch your idea yet:(
> When to register the I/O range? Is it done just after the successfully
> of_translate_address() during the children scanning?

No, you do it when first finding the bus itself, just like we do for
PCI host bridges.

> If yes, when a child is scanning, there is no range data in arm64_extio_ops. The
> addr_is_indirect_io() calling in of_get_isa_indirect_io() don't need. All we can
> check is just whether the address to be translated is IO and is under a parent
> device which has no 'ranges' property.

The children should only be scanned after the I/O range has been
registered for the parent.

> > Your current version has
> >
> > if (arm64_extio_ops->pfout) \
> > arm64_extio_ops->pfout(arm64_extio_ops->devpara,\
> > addr, value, sizeof(type)); \
> >
> > Instead, just subtract the start of the range from the logical
> > port number to transform it back into a bus-local port number:
> >
> > if (arm64_extio_ops->pfout) \
> > arm64_extio_ops->pfout(arm64_extio_ops->devpara,\
> > addr - arm64_extio_ops->start, value, sizeof(type)); \
> >
> I think there is some information needed sync.
> In the old patch-set, we don't bypass the pci_address_to_pio() after
> successfully of_translate_address(). In this way, we don't need to reserve any
> PIO space for our LPC since the logical port are from the same mapping
> algorithm. Based on this way, the port number in the device resource is logical
> one, then we need to subtract the start of the resource to get back the
> bus-local port.
> From V3, we don't apply the mapping based on pci_address_to_pio(), the
> of_translate_address() return the bus-local port directly and store into
> relevant device resource. So, in the current arm64_extio_ops->pfout(), the
> reverse translation don't need anymore. The input "addr" is bus-local port now.

Ok, so this would have to be changed again: If we want to support multiple
bus domains, of_translate_address() must translate between the bus specific
address and the general Linux I/O port number. Even without doing that,
it seems nicer to not overlap the range of the first PCI host bridge.