On Sun, Feb 25, 2018 at 5:28 PM, Feng Kan <fkan@xxxxxxx> wrote: > On Sun, Feb 25, 2018 at 1:29 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: >> On Sat, Feb 24, 2018 at 2:59 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote: >>> On Sat, Feb 24, 2018 at 10:47:26AM +0100, Rafael J. Wysocki wrote: >>>> On Sat, Feb 24, 2018 at 10:35 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: >>>> > On Sat, Feb 24, 2018 at 1:46 AM, Feng Kan <fkan@xxxxxxx> wrote: >>>> >> This is not a patch, but rather a question regarding the deferred >>>> >> probe's effect on PCIe PM ordering. This happens on our system >>>> >> which defer the probing of root bridge due to the IOMMU not being >>>> >> ready. Because of the deferred action, the bridge is moved to the >>>> >> end of the dpm_list which results in incorrect suspend and resume >>>> >> sequence. >>>> >> >>>> >> In the cases I have seen, the bridge is always reordered because of >>>> >> startup sequence. They are always place after the endpoint. If that >>>> >> is the case the following code should be able to prevent such cases. >>>> >> However, is there some cases here that would violate such situation? >>>> > >>>> > The code in dd.c assumes that the device being probed has no children >>>> > (or consumers, for that matter) and so it is safe to move it to the >>>> > end of the list. >>>> > >>>> > If the device has children (or consumers), moving it to the end of the >>>> > list by itself doesn't work, which is the case for you. >>>> > >>>> > You can try to replace the device_pm_move_last(dev) in >>>> > deferred_probe_work_func(struct() with device_reorder_to_tail(), but >>>> > that has to be called under device_links_read_lock/unloc () and >>>> > device_pm_lock/unloc() (in the right order). >>>> >>>> Alternatively, you can replace your !dev_is_pci(dev) check with a >>>> check for the presence of children or consumers and only move the >>>> device to the end of the PM list if there are not any. That would >>>> kind of make sense, but it may break other assumptions in the deferred >>>> probing mechanism which I don't recall ATM. >>>> >>>> Or avoid deferred probing of the host bridge driver entirely. I guess >>>> you can use it with limited functionality until the IOMMU driver is >>>> ready and switch over to the fully functional operation mode when that >>>> happens, but that would need to hook into the IOMMU code somehow. >>> >>> Or model the root bridge's dependency on the iommu using a device link: >>> https://www.kernel.org/doc/html/latest/driver-api/device_link.html >> >> Apparently, there are children registered under the bridge device >> before the driver for it is probed. > > Yes, so the order seems to be like this: > 1. root port and endporint is enumerated and added to dpm_list > 2. root port probed and deferred > 3. iommu probed and successful > 4. root port probed again and successful -> moved to last in dpm_list > 5. endpoint probed and successful > > I guess another approach would be to prevent 1 from happening by not > adding to dpm_list until the probe is successful. No, system-wide suspend/resume of PCIe devices is handled by the PCI bus type layer in part, so they have to be in dpm_list from the outset. Root ports, as their parents, need to be there before the endpoints.