linux-kernel - Re: [PATCH v2 2/4] PCI: pci-host-generic: Fix lookup of linux,pci-probe-only property

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Date:	Fri, 14 Aug 2015 17:43:25 +0100
From:	Will Deacon <will.deacon@....com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Marc Zyngier <Marc.Zyngier@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	"agraf@...e.de" <agraf@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] PCI: pci-host-generic: Fix lookup of
 linux,pci-probe-only property

On Fri, Aug 14, 2015 at 05:40:51PM +0100, Bjorn Helgaas wrote:
> On Fri, Aug 14, 2015 at 05:19:17PM +0100, Marc Zyngier wrote:
> > When pci-host-generic looks for the probe-only property, it seems
> > to trust the DT to be correctly written, and assumes that there
> > is a parameter to the property.
> > 
> > Unfortunately, this is not always the case, and some firmware expose
> > this property naked. The driver ends up making a decision based on
> > whatever the property pointer points to, which is likely to be junk.
> > 
> > Switch to the common of_pci.c implementation that doesn't suffer
> > from this problem.
> > 
> > Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> > ---
> >  drivers/pci/host/pci-host-generic.c | 9 +--------
> >  1 file changed, 1 insertion(+), 8 deletions(-)
> > 
> > diff --git a/drivers/pci/host/pci-host-generic.c b/drivers/pci/host/pci-host-generic.c
> > index 265dd25..545ff4e 100644
> > --- a/drivers/pci/host/pci-host-generic.c
> > +++ b/drivers/pci/host/pci-host-generic.c
> > @@ -210,7 +210,6 @@ static int gen_pci_probe(struct platform_device *pdev)
> >  	int err;
> >  	const char *type;
> >  	const struct of_device_id *of_id;
> > -	const int *prop;
> >  	struct device *dev = &pdev->dev;
> >  	struct device_node *np = dev->of_node;
> >  	struct gen_pci *pci = devm_kzalloc(dev, sizeof(*pci), GFP_KERNEL);
> > @@ -225,13 +224,7 @@ static int gen_pci_probe(struct platform_device *pdev)
> >  		return -EINVAL;
> >  	}
> >  
> > -	prop = of_get_property(of_chosen, "linux,pci-probe-only", NULL);
> > -	if (prop) {
> > -		if (*prop)
> > -			pci_add_flags(PCI_PROBE_ONLY);
> > -		else
> > -			pci_clear_flags(PCI_PROBE_ONLY);
> > -	}
> > +	of_pci_check_probe_only(of_chosen);
> 
> Do we need support for pci-probe-only in pci-host-generic at all?
> You're removing the use in amd-overdrive.dts, and there are no other
> DTs in the kernel tree that mention it.
> 
> If we can live without it, that would be nice.  It seems like a relic from
> days when we couldn't reliably assign resources.  (I'm not saying we can do
> that reliably even today, but I'd rather make it reliable than turn it
> off.)

Kvmtool certainly uses it (and generates its own DT, hence why you don't
see it in mainline). Not sure about qemu, though.

Will
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