linux-kernel - Re: [PATCH v2 0/3] Quirk Intel PCH root ports for ACS-like features

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Date:	Fri, 14 Feb 2014 14:43:20 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Don Dugger <donald.d.dugger@...el.com>
Subject: Re: [PATCH v2 0/3] Quirk Intel PCH root ports for ACS-like features

[+cc Don]

On Mon, Feb 03, 2014 at 02:27:27PM -0700, Alex Williamson wrote:
> v2:
>  - Remove bus #0 bug in filtering matching
>  - Add 2/3 introducing PCI_DEV_FLAGS_ACS_ENABLED_QUIRK, this gives
>    is better tracking and addresses the theoretical hotplug issue
>  - Update 3/3 for PCI_DEV_FLAGS_ACS_ENABLED_QUIRK
>  - Add dev_info to print regardless of whether we changes bits
>  - Add Intel cc
>
> As described in 3/3 many Intel root ports lack PCIe ACS capabilities
> which results in excessively large IOMMU groups.  Many of these root
> ports do provide isolation capabilities, we just need to use device
> specific mechanisms to enable and verify.  Long term, I hope we can
> round out this list (particularly to include X79 root ports) and
> more importantly, encourage proper PCIe ACS support in future
> products.  I'm really hoping we can get this in during the 3.14 cycle.
> Thanks,
>
> Alex
> ---
>
> Alex Williamson (3):
>       pci: Add device specific PCI ACS enable
>       pci: Add pci_dev_flag for ACS enable quirks
>       pci/quirks: Enable quirks for PCIe ACS on Intel PCH root ports

I applied these (with Don's ack for 3/3) to pci/virtualization.

I tried to figure out how to handle post-merge window patches.  Per
Documentation/development-process/2.Process, "[after -rc1], only patches
which fix problems should be submitted to the mainline," so one might
conclude that a fix for any sort of problem is allowed.  However,
Documentation/networking/netdev-FAQ.txt says "No new features get mainlined
after this [-rc1] -- only fixes to the rc1 content are expected," which is
how I've been operating.

In any case, these patches look more like new functionality (enabling a
non-standard ACS feature) than a bug fix to me, so my preference is to
merge them during the v3.15 merge window.

I understand the desire for v3.14, namely, "lots of Intel devices don't
support ACS, and that makes it hard for users to expose devices to
userspace with fine granularity, and waiting for v3.15 will mean another
two months."  But this problem is really of Intel's own making: if they'd
used standard ACS, or if they'd documented their non-standard mechanism,
this wouldn't be an issue.

Bjorn
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