linux-kernel - Re: [RFC 3/4] arm64: Do not call enable PCI resources when specify PCI_PROBE

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Message-ID: <20150623230539.GK7557@n2100.arm.linux.org.uk>
Date:	Wed, 24 Jun 2015 00:05:39 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Jason Cooper <jason@...edaemon.net>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Will Deacon <will.deacon@....com>,
	Liviu Dudau <liviu.dudau@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 3/4] arm64: Do not call enable PCI resources when specify
 PCI_PROBE_ONLY

On Wed, Jun 24, 2015 at 08:34:28AM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2014-09-29 at 12:17 -0600, Bjorn Helgaas wrote:
> > This seems like more than necessary, but I don't know all the history.
> > In particular, I don't know why PCI_PROBE_ONLY should make a
> > difference to things like claiming resources.
> 
> It shouldn't ... we created that option on ppc originally to avoid
> allocation/reallocation of resources. If they are bad, leave them bad,
> but it was never a question of disabling all these other things.
> 
> (Ok, the MRSS/MPS is debatable, but why not plumb the parent pointers
> and why not claim ? That doesn't make sense to me).

You could look back over the history of arch/arm/kernel/bios32.c and
see that it was introduced by Will Deacon when he stripped out the
ARM version in favour of the generic version, and was found to be
necessary then.

I think the question has to be asked (based upon what Ben's saying)
and what's identified in these commits as a failure case
(pci_enable_resource failing when PCI_PROBE_ONLY is enabled) -
why is the PCI core creating per-device resources which do not have
parents.

I've no idea on that; the only ARM boxes I have use the kernel's PCI
allocation, I don't have these boxes which want to use PCI_PROBE_ONLY
so it's something I have zero knowledge of.

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
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