From: Bjorn Helgaas <helgaas@kernel.org>
To: Sinan Kaya <okaya@codeaurora.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
linux-pci@vger.kernel.org, Zhou Wang <wangzhou1@hisilicon.com>,
Phil Edworthy <phil.edworthy@renesas.com>,
Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [RFC] ARM/ARM64 PCI_PROBE_ONLY platforms
Date: Fri, 29 Jan 2016 17:26:09 -0600 [thread overview]
Message-ID: <20160129232609.GB11085@localhost> (raw)
In-Reply-To: <569FCEA8.4020001@codeaurora.org>
On Wed, Jan 20, 2016 at 01:15:04PM -0500, Sinan Kaya wrote:
> Footnote: I remember reading somewhere that some BIOS want to keep track
> of where the endpoints are mapped. Reassigning the resources break such systems.
I agree, I think there are systems where the BIOS sets a PCI BAR value
and depends on that remaining untouched at run-time. For example, I'm
pretty sure there's x86 SMM code that logs errors to PCI management
devices. I think these systems are broken.
I don't think there's a way for firmware to tell the kernel "please
don't reassign these PCI resources." After handoff to the OS, I think
the OS owns all PCI resources and can reassign things as necessary,
subject only to a few constraints like _OSC. Certainly the OS has to
be able to write to BARs at least temporarily to learn their size. I
have no spec reference for this belief.
I don't have a good strategy for dealing with such systems, other
than:
- Keep firmware BAR assignments unless we have a reason to change
them
- Add quirks to set IORESOURCE_PCI_FIXED for specific BARs when we
know about issues
The new PCI "Enhanced Allocation" stuff might be a way for platforms
to do this more safely.
Bjorn
next prev parent reply other threads:[~2016-01-29 23:26 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-20 16:04 [RFC] ARM/ARM64 PCI_PROBE_ONLY platforms Lorenzo Pieralisi
2016-01-20 16:13 ` Sinan Kaya
2016-01-20 18:10 ` Lorenzo Pieralisi
2016-01-20 18:15 ` Sinan Kaya
2016-01-29 23:26 ` Bjorn Helgaas [this message]
2016-01-22 16:28 ` Phil Edworthy
2016-01-25 17:51 ` Lorenzo Pieralisi
2016-01-28 17:27 ` Lorenzo Pieralisi
2016-01-29 12:02 ` Gabriele Paoloni
2016-01-29 6:32 ` Pratyush Anand
2016-01-29 23:25 ` Bjorn Helgaas
2016-02-01 16:28 ` Lorenzo Pieralisi
2016-02-01 21:19 ` Bjorn Helgaas
2016-01-29 23:06 ` Bjorn Helgaas
2016-01-30 0:14 ` Sinan Kaya
2016-01-30 13:30 ` Bjorn Helgaas
2016-01-30 17:51 ` Okaya
2016-02-01 15:25 ` Lorenzo Pieralisi
2016-02-01 21:12 ` Bjorn Helgaas
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