On Wed, Jul 24, 2013 at 04:42:03PM -0400, Don Dutile wrote: > On 07/23/2013 06:35 PM, Bjorn Helgaas wrote: > >On Thu, Jul 11, 2013 at 03:03:27PM -0600, Alex Williamson wrote: > >>This provides interfaces for drivers to discover the visible PCIe > >>requester ID for a device, for things like IOMMU setup, and iterate > > > >IDs (plural) > > > a single device does not have multiple requester id's; > can have multiple tag-id's (that are ignored in this situation, but > can be used by switches for ordering purposes), but there's only 1/fcn > (except for those quirker pdevs!). Generally a device does not have multiple requester IDs, but the IOMMU may see one of several requester IDs for DMAs from a given device because bridges may take ownership of those transactions (sec 3.6.1.1 of the VT-d spec). Just to be clear, I envision this whole interface as being specifically for use by IOMMU drivers, so I'm only trying to provide what's necessary to build IOMMU mappings. > >>+ * pci_get_visible_pcie_requester - Get requester and requester ID for > >>+ * @requestee below @bridge > >>+ * @requestee: requester device > >>+ * @bridge: upstream bridge (or NULL for root bus) > >>+ * @requester_id: location to store requester ID or NULL > >>+ */ > >>+struct pci_dev *pci_get_visible_pcie_requester(struct pci_dev *requestee, > >>+ struct pci_dev *bridge, > >>+ u16 *requester_id) > > > >I'm not sure it makes sense to return a struct pci_dev here because > >there's no requirement that a requester ID correspond to an actual > >pci_dev. > > > well, I would expect the only callers would be for subsys (iommu's) > searching to find requester-id for a pdev, b/c if a pdev doesn't exist, > then the device (and requester-id) doesn't exist... :-/ > >>+ * pcie_for_each_requester - Call callback @fn on each devices and DMA source > >>+ * from @requestee to the PCIe requester ID visible > >>+ * to @bridge. > > > >Transactions from a device may appear with one of several requester IDs, > >but there's not necessarily an actual pci_dev for each ID, so I think the > ditto above; have to have a pdev for each id.... This *might* be true, but I don't think we should rely on it. For example: 00:1c.0 PCIe to PCI bridge to [bus 01] 01:01.0 PCI endpoint The bridge will take ownership of DMA transactions from the 01:01.0 endpoint. An IOMMU on bus 00 will see a bridge-assigned requester ID of 01:00.0 (subordinate bus number, devfn zero), but there is no 01:00.0 device. Maybe the rules of conventional PCI require a device zero (I don't remember), but even if they do, it's ugly to rely on that here because I don't think device 01:00.0 is relevant to mappings for device 01:01.0. Obviously we also have to be aware that 01:00.0 and 01:01.0 can't be isolated from each other, but I think that issue is separate from the question of what requester IDs have to be mapped to make 01:01.0 work. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
