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

[Lorenzo Pieralisi]

Hi Hanjun,

On Thu, Jun 04, 2015 at 10:28:17AM +0100, Hanjun Guo wrote:
> Hi Lorenzo,
> 
> On 2015???06???02??? 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:
> * System I/O space
> * System memory space
> * PCI configuration space
> * Embedded controller space
> * System Management Bus (SMBus) space
> * CMOS
> * PCI BAR Target
> * 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.

Us, by changing attitude and questioning features whose usefulness
is questionable. I will look into this and raise the point, I am not
thrilled by the idea of adding another set of PCI accessor functions
and drivers because we have to access a register through PCI before
enumerating the bus (and on arm64 this is totally useless since
we are not meant to support fixed HW anyway). Maybe we can make acpica
code use a "special" stub (ACPI specific, PCI configuration space address
space has restrictions anyway), I have to review this set in its
entirety to see how to do that (and I would kindly ask you to do
it too, before saying it is not possible to implement it).

Thanks,
Lorenzo
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