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 09:50:54 -0700
From:	Alexander Graf <agraf@...e.de>
To:	Will Deacon <will.deacon@....com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	"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 14.08.2015, at 09:43, Will Deacon <will.deacon@....com> wrote:
> 
> 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.

QEMU definitely doesn't do proble-only. Is this driver used on real PPC machines too? In that case you also won't see the dt, because it comes with the hardware ;).


Alex

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