linux-kernel - Re: [PATCH 3/3] PCI: Set pref for mem64 resource of pcie device

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Message-ID: <1428549459.18187.56.camel@kernel.crashing.org>
Date:	Thu, 09 Apr 2015 13:17:39 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	David Miller <davem@...emloft.net>,
	David Ahern <david.ahern@...cle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 3/3] PCI: Set pref for mem64 resource of pcie device

On Wed, 2015-04-08 at 17:06 -0700, Yinghai Lu wrote:
> On Wed, Apr 8, 2015 at 2:12 PM, Benjamin Herrenschmidt
> <benh@...nel.crashing.org> wrote:
> 
> > Thanks Bjorn. We can fix Yinghai patch for 4.2, it would be indeed handy
> > even for us to be able to support putting 64-bit NP BARs in prefetch
> > windows (For some SR-IOV adapters for example) too, but we need to do it
> > right.
> 
> Please check if you are ok with attached.

I'll let Bjorn be the final judge here but I am not fan of the way you
set/clear/set/clear the IORESOURCE_PREFETCH bit with
pci_set_pref_under_pref(). It's error prone and confusing, the code is
already barely readable as it is ...

I would rather you replace those various masks compares with a helper
that does something like pci_resource_compatible(parent_res, child_res),
which has the logic to test. That or a helper that does something like
pci_calc_compatible_res_flags() which returns a "flags" that has
PREFETCH set, which you use in place of res->flags in the various
allocation path.

As-is, your patch looks like a band-aid and smells like a hack :-)

Ben.

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