On Mon, Jan 30, 2017 at 11:56:23AM +0000, Gabriele Paoloni wrote: > Hi Keith > > I am looking at the current DPC implementation in: > http://lxr.free-electrons.com/source/drivers/pci/pcie/pcie-dpc.c > > > If my understanding is correct upon an incoming DPC event > the DPC IRQ handler will: > 1) stop and remove all the devices in the hierarchy under the > downstream port that raised the event > 2) wait for the data link to be inactive > 3) keep the downstream port status in DPC (in fact we set the DPC > trigger status again here: > http://lxr.free-electrons.com/source/drivers/pci/pcie/pcie-dpc.c#L55) > > Now looking at the specs we have (section 6.2.10): > "After software releases the Downstream Port from DPC, the associated Link > will normally attempt to retrain. Software can use Data Link Layer State > Changed interrupts, DL_Active ERR_COR signaling, or both, to signal when > the Link reaches the DL_Active state again" > > So if my understanding is correct in the current Linux implementation > It is not possible to recover a PCIe hierarchy from a DPC event, is it correct? > If this is correct, shouldn't we change the current implementation to release > the port from DPC and re-scan the secondary bus after the conditions described > in "PCIe 3.1 section 6.2.10" are met (I.e. <<Data Link Layer Link Active bit in > the 15 Link Status register reads 0b>> and if it is a root port also <<until > the DPC RP Busy bit reads 0b>>) ? That sounds reasonable. In all testing I've done, DPC events were triggered as part of a hot-plug event, so the secondary bus rescan would automatically happen when a device is hot inserted. The DPC driver didn't need to initiate the rescan in that case. But surprise removal is certainly not the only condition DPC can contain a port, so I agree with you that we may require pcie-dpc initiate a rescan after releasing the port from containment. I also agree on needing to poll RP busy for root ports. Do you want to send patches for these? I could also write them up, but I don't have a DPC capable root port to test that part. Thanks, Keith -- 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
