linux-kernel - Re: [PATCH 02/11] PCI: Try to allocate mem64 above 4G at first

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Message-ID: <CAE9FiQV7jpBWkcXy2vgixnxx2fhid28Wj0iHAhGkVVdQn6epNQ@mail.gmail.com>
Date:	Mon, 4 Jun 2012 19:37:06 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	David Miller <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Newbury <steve@...wbury.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] PCI: Try to allocate mem64 above 4G at first

On Sun, Jun 3, 2012 at 6:05 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Fri, Jun 1, 2012 at 4:30 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> On Tue, May 29, 2012 at 1:50 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>>
>>> The bus-side address space should not be more than 32 bits no matter
>>> what.  As Bjorn indicates, you seem to be mixing up bus and cpu
>>> addresses all over the place.
>>
>> please check update patches that is using converted pci bus address
>> for boundary checking.
>
> What problem does this fix?  There's significant risk that this
> allocation change  will make us trip over something, so it must fix
> something to make it worth considering.

If we do not enable that, we would not find the problem.

On one my test setup that _CRS does state 64bit resource range,
but when I clear some device resource manually and let kernel allocate
high, just then find out those devices does not work with drivers.
It turns out _CRS have more big range than what the chipset setting states.
with fixing in BIOS, allocate high is working now on that platform.

>
> Steve's problem doesn't count because that's a "pci=nocrs" case that
> will always require special handling.

but pci=nocrs is still supported, even some systems does not work with
pci=use_crs

> A general solution is not
> possible without a BIOS change (to describe >4GB apertures) or a
> native host bridge driver (to discover >4GB apertures from the
> hardware).  These patches only make Steve's machine work by accident
> -- they make us put the video device above 4GB, and we're just lucky
> that the host bridge claims that region.

Some bios looks enabling the non-stated range default to legacy chain.
Some bios does not do that. only stated range count.
So with pci=nocrs we still have some chance to get allocate high working.

>
> One possibility is some sort of boot-time option to force a PCI device
> to a specified address.  That would be useful for debugging as well as
> for Steve's machine.

yeah, how about

pci=alloc_high

and default to disabled ?

Thanks

Yinghai
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