On Wed, May 25, 2016 at 01:21:12PM -0400, Sinan Kaya wrote: > Hi Bjorn, > > OK. I see that we are dealing with two different questions. > > > I thought you were talking about booting with > > "pcie_aspm.policy=powersave", where pcie_aspm_set_policy() sets > > aspm_policy = POLICY_POWERSAVE, then configures each link with > > ASPM_STATE_ALL. But pcie_config_aspm_link() does AND the desired > > state (ASPM_STATE_ALL) with link->aspm_capable, which only has > > ASPM_STATE_L0S set if both the upstream and downstream components > > advertised PCIE_LINK_STATE_L0S. > > This path is very complicated, but I don't *think* it will enable L0s > > if the other end of the link doesn't support it. > > Thanks for clarifying this. You are saying that if one side of the > link doesn't support L0s, Linux doesn't enable L0s on the other side. > This makes sense. > > I think there is a confusion between what supported means vs. when > L0s can be enabled on which side of the link. > > You clarified the supported case above that code will not enable > L0s if the other side doesn't support L0s. > > > > Now we enable the downstream component's transmitter to enter L0s. > > Per PCIe spec r3.0, sec 7.8.7, the receiver, i.e., the upstream > > component, must be capable of entering L0s even when its transmitter > > is disabled from entering L0s. > > Let's assume that both sides actually support L0s but the link parameters > on one side is not compatible. > > You are saying that it is OK to enable L0s on just one side of the > link as long as both sides support L0s. I'm not sure what you mean by the link parameters not being compatible, but I think it is legal to enable L0s on only one direction. > This part is a little bit misleading. I had HW people telling me > that both sides need to enable L0s at about the same time. I don't remember seeing anything like that in the spec. Do they have a pointer? "At about the same time" is too hand-wavey to be useful to software. > I'm actually seeing Linux enabling L0s on one side only as you > described and both supports L0s. -- 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
