Re: [PATCH v4 0/5] PCI: Add support for PCI Enhanced Allocation "BARs"

[David Daney <ddaney.cavm@gmail.com>]

On 10/05/2015 04:05 PM, Sean O. Stalley wrote:
> On Fri, Oct 02, 2015 at 08:16:48PM -0700, Yinghai Lu wrote:
>> On Fri, Oct 2, 2015 at 3:37 PM, David Daney <ddaney.cavm@gmail.com> wrote:
>>> From: David Daney <david.daney@cavium.com>
>>>
>>> PCI Enhanced Allocation is a new method of allocating MMIO & IO
>>> resources for PCI devices & bridges. It can be used instead
>>> of the traditional PCI method of using BARs.
>>>
>>> EA entries are hardware-initialized to a fixed address.
>>> Unlike BARs, regions described by EA are cannot be moved.
>>> Because of this, only devices which are permanently connected to
>>> the PCI bus can use EA. A removable PCI card must not use EA.
>>>
>>> The Enhanced Allocation ECN is publicly available here:
>>> https://www.pcisig.com/specifications/conventional/ECN_Enhanced_Allocation_23_Oct_2014_Final.pdf
>>
>> Looks like the EA will support more than just fixed address later.
>>
>> "Enhanced Allocation is an optional Conventional PCI Capability that
>> may be implemented by
>> Functions to indicate fixed (non reprogrammable) I/O and memory ranges
>> assigned to the
>> Function, as well as supporting new resource “type” definitions and
>> future extensibility to also
>> support reprogrammable allocations."
>>
>> so I would prefer to think more to make frame configurable to leave
>> space for that.
>>
>> Bjorn,
>>
>> I wonder if we need to revive the add-on resource support patchset
>> that i suggested couple years ago,
>> so we can extend it to support EA features.
>>
>> URL: https://lkml.org/lkml/2012/3/19/86
>>
>> Thanks
>>
>> Yinghai
>
> This might be useful for fixed resources as well.
>
> For some BEI values, EA allows for an arbitrary number of EA entries.

I think this is true only for BEI = 6 which is for type-1 config space 
only (i.e. for bridges)

I am thinking about splitting out the bridge part of the patch set, as 
my systems work fine without explicitly assigning bridge resources via 
EA.  That would allow us to more forward with the patches that are less 
controversial, and spend more time hashing out the proper approach to 
take with bridges.

> For PF & VF resource ranges, it allows 2 ranges.

I don't really understand what you are saying here.  My reading of the 
spec. is that BEI[0..5] are PF BARs and each may have any of the 
properties that are allowed for normal BARs (io, memory-nonprefetchable, 
memory-prefetchable).  BEI[9..14] are VF BARs, and likewise may have any 
of the properties that are alloed for normal VF bars 
(memory-nonprefetchable, memory-prefetchable)

I guess in theory EA allows you to allocate 6 64-bit BARs, where you 
would be limited to only 3 64-bit normal BARs


> (one below the 4GB boundry, and one above).
> I don't think the current pci_dev struct can handle that many resources.
>
> -Sean
>