[RFC PATCH 1/5] pci/p2p: add a function to test peer to peer capability

[Logan Gunthorpe]

On 2019-01-29 12:44 p.m., Greg Kroah-Hartman wrote:
> On Tue, Jan 29, 2019 at 11:24:09AM -0700, Logan Gunthorpe wrote:
>>
>>
>> On 2019-01-29 10:47 a.m., jglisse at redhat.com wrote:
>>> +bool pci_test_p2p(struct device *devA, struct device *devB)
>>> +{
>>> +	struct pci_dev *pciA, *pciB;
>>> +	bool ret;
>>> +	int tmp;
>>> +
>>> +	/*
>>> +	 * For now we only support PCIE peer to peer but other inter-connect
>>> +	 * can be added.
>>> +	 */
>>> +	pciA = find_parent_pci_dev(devA);
>>> +	pciB = find_parent_pci_dev(devB);
>>> +	if (pciA == NULL || pciB == NULL) {
>>> +		ret = false;
>>> +		goto out;
>>> +	}
>>> +
>>> +	tmp = upstream_bridge_distance(pciA, pciB, NULL);
>>> +	ret = tmp < 0 ? false : true;
>>> +
>>> +out:
>>> +	pci_dev_put(pciB);
>>> +	pci_dev_put(pciA);
>>> +	return false;
>>> +}
>>> +EXPORT_SYMBOL_GPL(pci_test_p2p);
>>
>> This function only ever returns false....
> 
> I guess it was nevr actually tested :(
> 
> I feel really worried about passing random 'struct device' pointers into
> the PCI layer.  Are we _sure_ it can handle this properly?

Yes, there are a couple of pci_p2pdma functions that take struct devices
directly simply because it's way more convenient for the caller. That's
what find_parent_pci_dev() takes care of (it returns false if the device
is not a PCI device). Whether that's appropriate here is hard to say
seeing we haven't seen any caller code.

Logan