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

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Message-ID: <20151006154747.GA2559@sean.stalley.intel.com>
Date:	Tue, 6 Oct 2015 08:47:47 -0700
From:	"Sean O. Stalley" <sean.stalley@...el.com>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rafał Miłecki <zajec5@...il.com>,
	linux-api@...r.kernel.org, Rajat Jain <rajatxjain@...il.com>,
	"gong.chen@...ux.intel.com" <gong.chen@...ux.intel.com>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH v4 0/5] PCI: Add support for PCI Enhanced Allocation
 "BARs"

On Mon, Oct 05, 2015 at 06:17:20PM -0700, David Daney wrote:
> 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@...il.com> wrote:
> >>>From: David Daney <david.daney@...ium.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)

It's true for a BEI of 6 or 7.

>From the ECN (specifically section 6.9.1.3):

Rules for use of BEI field:
	...
	It is permitted for an arbitrary number of entries to assign a BEI of 6 or 7.

> 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.

I like this idea. Adding support for Endpoints will be much simpler than
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)


>From the ECN (specifically section 6.9.1.3):

Rules for use of BEI field:
...

For Memory or I/O BARs where the Primary or Secondary Property is 00h, 01h or
02h, it is permitted to assign the same BEI in the range of 0-5 once for a range where
Base + MaxOffset is below 4GB, and again for a range where Base + MaxOffset is
greater than 4GB; It is not otherwise permitted to assign the same BEI in the range 0-
5 for more than one entry.

For Virtual Function BARs where the Primary or Secondary Property is 03h or 04h it
is permitted to assign the same BEI in the range of 0-5 once for a range where Base +
MaxOffset is below 4GB, and again for a range where Base + MaxOffset is greater
than 4GB; It is not otherwise permitted to assign the same BEI in the range 0-5 for
more than one VF entry.

(Theres a typo in the VF rule. I think the '0-5' range should be '9-14' for VFs)

> 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

I guess so, I never thought about that.

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

Let me know if you want any help with the patchset. I'll do what I can.
I'm in today, but I'm out Wed-Fri this week.

-Sean
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