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SubjectRe: [PATCH 02/11] PCI: Try to allocate mem64 above 4G at first
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On Tue, May 29, 2012 at 12:23 PM, Bjorn Helgaas <bhelgaas@google.com> wrote:
> On Tue, May 29, 2012 at 12:17 PM, Yinghai Lu <yinghai@kernel.org> wrote:
>> On Tue, May 29, 2012 at 10:57 AM, H. Peter Anvin <hpa@zytor.com> wrote:
>>> On 05/29/2012 10:55 AM, Yinghai Lu wrote:
>>>>
>>>> x86 are using 16bits.
>>>>
>>>> some others use 32 bits.
>>>> #define IO_SPACE_LIMIT 0xffffffff
>>>>
>>>> ia64 and sparc are using 64bits.
>>>> #define IO_SPACE_LIMIT               0xffffffffffffffffUL
>>>>
>>>> but pci only support 16bits and 32bits.
>>>>
>>>> maybe later we can add
>>>> PCI_MAX_RESOURCE_16
>>>>
>>>> to handle 16bits and 32bit io ports.
>>>>
>>>
>>> Shouldn't this be dealt by root port apertures?
>>>
>>
>> pci bridge could support 16bits and 32bits io port.
>> but we did not record if 32bits is supported.
>>
>> so during allocating, could have allocated above 64k address to non
>> 32bit bridge.
>>
>> but  x86 is ok, because ioport.end always set to 0xffff.
>> other arches with IO_SPACE_LIMIT with 0xffffffff or
>> 0xffffffffffffffffUL may have problem.
>
> I think current IO_SPACE_LIMIT usage is a little confused.  The
> "ioport_resource.end = IO_SPACE_LIMIT" in kernel/resource.c refers to
> a CPU-side address, not a bus address.  Other uses, e.g., in
> __pci_read_base(), apply it to bus addresses from BARs, which is
> wrong.  Host bridges apply I/O port offsets just like they apply
> memory offsets.  The ia64 IO_SPACE_LIMIT of 0xffffffffffffffffUL means
> there's no restriction on CPU-side I/O port addresses, but any given
> host bridge will translate its I/O port aperture to bus addresses that
> fit in 32 bits.
>
> None of this is really relevant to the question I asked, namely, "why
> Yinghai's patch doesn't limit I/O BAR values to 32 bits?"  That
> constraint is clearly a requirement because I/O BARs are only 32 bits
> wide, but I don't think it needs to be enforced in the code here.  The
> host bridge or upstream P2P bridge apertures should already take care
> of that automatically.  I don't think the 16- or 32-bitness of P2P
> bridge apertures is relevant here, because the I/O resources available
> on the secondary bus already reflect that.
>
> After all that discussion, I think my objection here boils down to
> "you shouldn't change the I/O BAR constraints in a patch that claims
> to allocate 64-bit *memory* BARs above 4GB."
>
> I think the code below is still the clearest way to set the constraints:
>
>   if (res->flags & IORESOURCE_MEM_64) {
>       start = (resource_size_t) (1ULL << 32);
>       end = PCI_MAX_RESOURCE;
>   } else {
>       start = 0;
>       end = PCI_MAX_RESOURCE_32;
>   }
>
> It's not strictly necessary to limit I/O BARs to PCI_MAX_RESOURCE_32
> because host bridge apertures should already enforce that, but I think
> the code above just makes it clearer.


ok, please check the version, that put back PCI_MAX_RESOURCE_32 for io ports.

also RFC to limit for 16 bit ioport handling. only help other arches
that does support 32bit ioports but have bridges only support 16bit io
ports.

Thanks

Yinghai
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