On Fri, May 17, 2013 at 3:12 PM, Phillip Susi <psusi@xxxxxxxxxx> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 5/17/2013 4:24 PM, Bjorn Helgaas wrote: >> Oh, wait a minute... You mentioned the radeon driver. The Radeon >> device in your system is at 01:00.0, and that is below the 00:01.0 >> bridge that said "ASPM unknown." If the bridge leading to the >> Radeon device doesn't support ASPM, then of course, we won't be >> able to turn on ASPM for it. > > That's what I was asking about before when I said surely the bridge > higher up doesn't have to have aspm enabled in order to enable it on > the downstream link? A link has two ends. Both ends have to support ASPM in order for it to work. But ASPM on a particular link has no dependency on things elsewhere in the hierarchy. >> That doesn't explain why we don't turn on ASPM for the *other* >> devices (03:00.0, 05:00.0, 06:00.0, 09:00.0) though. > > 00:01.0 says it is the root complex, so wouldn't that make it upstream > of *everything*? As I understand it, the root complex is built into > the CPU and has 16 lanes going to the video slot, and another 4 lanes > running at gen3 speed that Intel calls the DMI that goes to the PCH, > which has some internal functions, and bridges to another 20 pcie lanes. > > Since the root complex is built into the cpu, I wouldn't think ASPM > could possibly make sense on it, so it showing that it doesn't support > ASPM makes sense to me. That doesn't seem like it should preclude > using ASPM on the link down to the video card. The link between 00:01.0 and 01:00.0 apparently only supports ASPM on one end (the downstream end), so ASPM won't work on it. 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
