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

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Message-ID: <CAE9FiQXT0ux42gQ+DhpVv2K=BR4jC++LmNdCSLiK4Wy0BhL=HQ@mail.gmail.com>
Date:	Fri, 2 Oct 2015 20:16:48 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	David Daney <ddaney.cavm@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Sean O. Stalley" <sean.stalley@...el.com>
Cc:	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 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
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