Re: [PATCH 05/11] x86, pci, acpi: Move arch-agnostic MMCONFIG (aka ECAM) and ACPI code out of arch/x86/ directory

[Hanjun Guo]

Hi Lorenzo,

On 2015å06æ02æ 21:32, Lorenzo Pieralisi wrote:
> On Wed, May 27, 2015 at 09:06:26AM +0100, Tomasz Nowicki wrote:
> > On 26.05.2015 19:08, Will Deacon wrote:
> > > On Tue, May 26, 2015 at 01:49:18PM +0100, Hanjun Guo wrote:
> > > > From: Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxx>
> > > >
> > > > ECAM standard and MCFG table are architecture independent and it makes
> > > > sense to share common code across all architectures. Both are going to
> > > > corresponding files - ecam.c and mcfg.c
> > > >
> > > > While we are here, rename pci_parse_mcfg to acpi_parse_mcfg.
> > > > We already have acpi_parse_mcfg prototype which is used nowhere.
> > > > At the same time, we need pci_parse_mcfg been global so acpi_parse_mcfg
> > > > can be used perfectly here.
> > > >
> > > > Signed-off-by: Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxx>
> > > > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> > > > Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
> > > > ---
> > > >    arch/x86/Kconfig               |   3 +
> > > >    arch/x86/include/asm/pci_x86.h |  33 ------
> > > >    arch/x86/pci/acpi.c            |   1 +
> > > >    arch/x86/pci/mmconfig-shared.c | 244 +---------------------------------------
> > > >    arch/x86/pci/mmconfig_32.c     |   1 +
> > > >    arch/x86/pci/mmconfig_64.c     |   1 +
> > > >    arch/x86/pci/numachip.c        |   1 +
> > > >    drivers/acpi/Makefile          |   1 +
> > > >    drivers/acpi/mcfg.c            |  57 ++++++++++
> > > >    drivers/pci/Kconfig            |   7 ++
> > > >    drivers/pci/Makefile           |   5 +
> > > >    drivers/pci/ecam.c             | 245 +++++++++++++++++++++++++++++++++++++++++
> > >
> > > Why can't we make use of the ECAM implementation used by pci-host-generic
> > > and drivers/pci/access.c?
> >
> > We had that question when I had posted MMCFG patch set separately,
> > please see:
> > https://lkml.org/lkml/2015/3/11/492
>
> Yes, but the real question is, why do we need to have PCI config space
> up and running before a bus struct is even created ? I think the reason is
> the PCI configuration address space format (ACPI 6.0, Table 5-27, page
> 108):
>
> "PCI Configuration space addresses must be confined to devices on
> PCI Segment Group 0, bus 0. This restriction exists to accommodate
> access to fixed hardware prior to PCI bus enumeration".
>
> On HW reduced platforms I do not even think this is required at all,
> we have to look into this to avoid code duplication that might well
> turn out useless.

This is only for the fixed hardware, which will be not available for
ARM64 (reduced hardware mode), but in Generic Hardware Programming
Model, we using OEM-provided ACPI Machine Language (AML) code to access
generic hardware registers, this will be available for reduced hardware
too.

So in ACPI spec, it says: (ACPI 6.0 page 66, last paragraph)

ACPI defines eight address spaces that may be accessed by generic
hardware implementations. These include:
â System I/O space
â System memory space
â PCI configuration space
â Embedded controller space
â System Management Bus (SMBus) space
â CMOS
â PCI BAR Target
â IPMI space

So if any device using the PCI address space for control, such
as a system reset control device, its address space can be reside
in PCI configuration space (who can prevent a OEM do that crazy
thing? :) ), and it should be accessible before the PCI bus is
created.

Thanks
Hanjun
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