Re: [PATCH 3/6] x86, acpi, pci: Move PCI config space accessors.

[Rob Herring]

On Wed, Feb 18, 2015 at 12:27 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> On Tue, Feb 17, 2015 at 02:03:01PM +0100, Tomasz Nowicki wrote:
>> On 11.12.2014 00:17, Bjorn Helgaas wrote:
>> >On Wed, Nov 19, 2014 at 05:04:48PM +0100, Tomasz Nowicki wrote:
>> >>We are going to use mmio_config_{} name convention across all architectures.
>> >
>> >mmio_config_*() are workarounds for an AMD Fam10h defect [1].  I would prefer
>> >not to extend these names to other architectures, because they should be
>> >able to use readb()/writeb()/etc. directly, as we did on x86 before
>> >3320ad994afb ("x86: Work around mmio config space quirk on AMD Fam10h").
>> >
>> >In fact, it would be nice if we could use readb()/writeb()/etc. on x86, and
>> >only use mmio_config_*() when we're on AMD Fam10h.  Maybe there could be a
>> >"struct pci_raw_ops pci_mmcfg_amd_fam10h" that used mmio_config_*(), and we
>> >could set raw_pci_ext_ops to those ops instead of the default ones when
>> >we're on AMD Fam10h.  Then x86 should be able to use the generic
>> >readb()-based ops on most platforms.
>>
>> While I do agree we should use readb()/writeb()... methods, I am not
>> sure there is a nice way to use mmio_config_*() exclusively for AMD
>> Fam10h. For x86, right now, we have three PCI config accessors sets:
>> mmconfig_32.c, mmconfig_64.c, numachip.c and each are different. So
>> one pci_mmcfg_amd_fam10h pci_raw_ops is not enough. I am thinking of
>> having additional structure (integrated with "struct
>> pci_mmcfg_region") that keeps MMIO accessors where readb()/writeb()
>> would be the default one. For AMD Fam10h case we could tweak it as
>> necessary. What do you thing Bjorn?
>
> It's OK if we use mmio_config_*() for all x86 (not just AMD Fam10h); that's
> what we do today.  It'd be *nicer* if we could use the workaround only for
> Fam10h, but if it complicates the code, don't bother.
>
> My main point is that I think your v1 posting requires every arch to
> implement mmio_config_*(), and they will all be the same.  If an arch
> doesn't require a workaround, it shouldn't have to supply anything and we
> should default to readb/writeb/etc.

Perhaps the abstraction needs to move up a level to pci_ops functions.
Then x86 can use the generic ones I added and AMD can use custom ones.

BTW, there are some cases on MIPS that need special accessors. It's
mainly a function of whether the accessors need to do endian swapping
or not.

Rob
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