Re: [Patch v7 4/7] PCI/ACPI: Add interface acpi_pci_root_create()

From: Lorenzo Pieralisi
Date: Wed Nov 11 2015 - 12:46:04 EST

On Tue, Nov 10, 2015 at 01:50:46PM +0800, Jiang Liu wrote:


> >> In particular, I would like to understand, for an eg DWordIO descriptor,
> >> what Range Minimum, Range Maximum and Translation Offset represent,
> >> they can't mean different things depending on the SW parsing them,
> >> this totally defeats the purpose.
> >
> > I have no clue about what those mean in ACPI though.
> >
> > Generally speaking, each PCI domain is expected to have a (normally 64KB)
> > range of CPU addresses that gets translated into PCI I/O space the same
> > way that config space and memory space are handled.
> > This is true for almost every architecture except for x86, which uses
> > different CPU instructions for I/O space compared to the other spaces.
> >
> >> By the way, ia64 ioremaps the translation_offset (ie new_space()), so
> >> basically that's the CPU physical address at which the PCI host bridge
> >> map the IO space transactions), I do not think ia64 is any different from
> >> arm64 in this respect, if it is please provide an HW description here from
> >> the PCI bus perspective here (also an example of ia64 ACPI PCI host bridge
> >> tables would help).
> >
> > The main difference between ia64 and a lot of the other architectures (e.g.
> > sparc is different again) is that ia64 defines a logical address range
> > in terms of having a small number for each I/O space followed by the
> > offset within that space as a 'port number' and uses a mapping function
> > that is defined as
> >
> > static inline void *__ia64_mk_io_addr (unsigned long port)
> > {
> > struct io_space *space = &io_space[IO_SPACE_NR(port)];
> > return (space->mmio_base | IO_SPACE_PORT(port););
> > }
> > static inline unsigned int inl(unsigned long port)
> > {
> > return *__ia64_mk_io_addr(port);
> > }
> >
> > Most architectures allow only one I/O port range and put it at a fixed
> > virtual address so that inl() simply becomes
> >
> > static inline u32 inl(unsigned long addr)
> > {
> > return readl(PCI_IOBASE + addr);
> > }
> >
> > which noticeably reduces code size.
> >
> > On some architectures (powerpc, arm, arm64), we then get the same simplified
> > definition with a fixed virtual address, and use pci_ioremap_io() or
> > something like that to to map a physical address range into this virtual
> > address window at the correct io_offset;
> Hi all,
> Thanks for explanation, I found a way to make the ACPI resource
> parsing interface arch neutral, it should help to address Lorenzo's
> concern. Please refer to the attached patch. (It's still RFC, not tested
> yet).

If we go with this approach though, you are not adding the offset to
the resource when parsing the memory spaces in acpi_decode_space(), are we
sure that's what we really want ?

In DT, a host bridge range has a:

- CPU physical address
- PCI bus address

We use that to compute the offset between primary bus (ie CPU physical
address) and secondary bus (ie PCI bus address).

The value ending up in the PCI resource struct (for memory space) is
the CPU physical address, if you do not add the offset in acpi_decode_space
that does not hold true on platforms where CPU<->PCI offset != 0 on ACPI,
am I wrong ?

Overall I think the point is related to ioport_resource and its check
in acpi_pci_root_validate_resources() which basically that's the
problem that started this thread.

On arm64, IO_SPACE_LIMIT is 16M, which, AFAIK is a kernel limit, not
a HW one. Comparing the resources parsed from the PCI bridge _CRS against
the range 0..IO_SPACE_LIMIT is not necessarily meaningful (or at least
not meaningful in its current form), on ia64 it works because IO_SPACE_LIMIT
is bumped up to 4G, that's the reason why adding the offset to the ACPI IO
resources work on ia64 as far as I understand.

And that's why I pulled Arnd in this discussion since he knows better
than me: what does ioport_resource _really_ represent on ARM64 ? It seems
to me that it is a range of IO ports values (ie a window that defines
the allowed offset in the virtual address space allocated to PCI IO) that
has _nothing_ to do with the CPU physical address at which the IO space is
actually mapped.

To sum it up for a, say, DWordIo/Memory descriptor:

- AddressMinimum, AddressMaximum represent the PCI bus addresses defining
the resource start..end
- AddressTranslation is the offset that has to be added to AddressMinimum
and AddressMaximum to get the window in CPU physical address space


- Either we go with the patch attached (but please check my comment on
the memory spaces)
- Or we patch acpi_pci_root_validate_resources() to amend the way
IORESOURCE_IO is currently checked against ioport_resource, it can't
work on arm64 at present, I described why above

Thoughts appreciated it is time we got this sorted and thanks for
the patch.

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