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 Thanks, Lukas
