On Thu, May 20, 2021 at 01:54:05PM +0200, Rafael J. Wysocki wrote: > On Thu, May 20, 2021 at 1:27 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > On Wed, May 19, 2021 at 9:48 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > On Wed, May 19, 2021 at 09:12:26PM +0200, Rafael J. Wysocki wrote: > > > > The problem is related to the fact that in s2idle the platform > > > > firmware does not finalize the suspend transition and, consequently, > > > > it doesn't initiate the resume transition. Therefore whatever power > > > > state the device was left in during suspend must be dealt with during > > > > the subsequent resume. Hence, if whatever is done by SXIO/SXFP/SXLF > > > > in the suspend path cannot be reversed in the resume path by the > > > > kernel (because there is no known method to do that), they should not > > > > be invoked. And that's exactly because the platform firmware will not > > > > finalize the suspend transition which is indicated by > > > > PM_SUSPEND_FLAG_FW_SUSPEND being unset. > > > > > > How can we connect "if (!pm_suspend_via_firmware())" in this patch > > > with the fact that firmware doesn't finalize suspend (and consequently > > > does not reverse things in resume)? > > > > > > I don't see any use of pm_suspend_via_firmware() or > > > PM_SUSPEND_FLAG_FW_SUSPEND that looks relevant. > > > > First of all, there is a kerneldoc comment next to > > pm_suspend_via_firmware() which is relevant. Especially the last > > paragraph of that comment applies directly to the case at hand IMV. I do read kerneldoc, but I *rely* on the code, and it's nice when I can match up the kerneldoc with what the code is doing :) Part of my confusion is that "passing control to platform firmware" isn't particularly useful in itself because it doesn't give a clue about what firmware is *doing*. Without knowing what it does, we can't reason about how kernel's actions interact with firmware's actions. > BTW, the problem at hand is not that s2idle in particular needs to be > treated in a special way (this appears to be the source of all > confusion here). The problem is that the kernel cannot undo the > SXIO/SXFP/SXLF magic without passing control to the platform firmware. I assume this is really a case of "the kernel doesn't know *what* to do, but platform firmware does," so in principle the kernel *could* undo the SXIO/SXFP/SXLF magic if it knew what to do. > And "passing control to the platform firmware" doesn't mean "executing > some AML" here, because control remains in the kernel when AML is > executed. "Passing control to the platform firmware" means letting > some native firmware code (like SMM code) run which happens at the end > of S2/S3/S4 suspend transitions and it does not happen during S1 > (standby) and s2idle suspend transitions. > > That's why using SXIO/SXFP/SXLF is only valid during S2/S3/S4 suspend > transitions and it is not valid during s2idle and S1 suspend > transitions (and yes, S1 is also affected, so s2idle is not special in > that respect at all). > > IMO the changelog of the patch needs to be rewritten, but the code > change made by it is reasonable. So IIUC the comment should say something like: SXIO/SXFP/SXLF turns off power to the Thunderbolt controller. We don't know how to turn it back on again, but firmware does, so we can only use SXIO/SXFP/SXLF if we're suspending via firmware. Actually, it sounds like the important thing is that we rely on the firmware *resume* path to turn on the power again. pm_resume_via_firmware() *sounds* like it would be appropriate, but the kerneldoc says that's for use after resume, and it tells us whether firmware has *already* handled the wakeup event. And PM_SUSPEND_FLAG_FW_RESUME isn't set until after we've run these suspend_late fixups, so it wouldn't work here. Bjorn
