On Thu, Jan 11, 2024 at 01:20:48PM -0500, Jim Quinlan wrote: > On Thu, Jan 11, 2024 at 12:28 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Mon, Nov 13, 2023 at 01:56:06PM -0500, Jim Quinlan wrote: > > > Previously, this driver always set the mode to "no-l1ss", as almost all > > > STB/CM boards operate in this mode. But now there is interest in > > > activating L1SS power savings from STB/CM customers, which requires "aspm" > > > mode. > > > > I think this should read "default" mode, not "aspm" mode, since "aspm" > > is not a mode implemented by this patch, right? > > Correct. Thanks, I changed that locally. > > > In addition, a bug was filed for RPi4 CM platform because most > > > devices did not work in "no-l1ss" mode. > > > > I think this refers to bug 217276, mentioned below? > > I guess you are saying I should put a footnote marker there. I added a hint here. > > > Note: Since L1 substates are now possible, a modification was made > > > regarding an internal bus timeout: During long periods of the PCIe RC HW > > > being in an L1SS sleep state, there may be a timeout on an internal bus > > > access, even though there may not be any PCIe access involved. Such a > > > timeout will cause a subsequent CPU abort. > > > > This sounds scary. If a NIC is put in L1.2, does this mean will we > > see this CPU abort if there's no traffic for a long time? What is > > needed to avoid the CPU abort? > > I don't think this happens in normal practice as there are a slew > of low-level TLPs and LTR messages that are sent on a regular > basis. OK, I'll have to take your word for this. I don't know enough about PCIe to know what sort of periodic transmissions are required when a device is idle. LTR messages are required when endpoint service requirements change, but I wouldn't expect those if the device is idle. > The only time this timeout occured is when a major customer > was doing a hack: IIRC, their endpoint device has to reboot itself > after link-up and driver probe, so it goes into L1.2 to execute > this to reboot and while doing so the connection is completely > silent. > > What does this mean for users? L1SS is designed for long periods of > > the device being idle, so this leaves me feeling that using L1SS is > > unsafe in general. Hopefully this impression is unwarranted, and all > > we need is some clarification here. > > I don't think it will affect most users, if any. I'll try to get this into -next today or tomorrow. Bjorn
