On Monday 05 January 2009, Pavel Machek wrote: > Hi! > > > Subject: PCI PM: Avoid touching devices behind bridges in unknown state (rev. 2) > > From: Rafael J. Wysocki <rjw@xxxxxxx> > > > > It generally is better to avoid accessing devices behind bridges that > > may not be in the D0 power state, because in that case the bridges' > > secondary buses may not be accessible. For this reason, during the > > early phase of resume (ie. with interrupts disabled), before > > restoring the standard config registers of a device, check the power > > state of the bridge the device is behind and postpone the restoration > > of the device's config space, as well as any other operations that > > would involve accessing the device, if that state is not D0. > > I'm not sure if this is good idea. > > Either pci config space needs to be restored early, or it can wait. > > Sometimes restoring it early and sometimes restoring it late seems > harmful: it will make code harder to understand and harder to test. Unfortunately, we need to restore it early at least for some devices (bridges and PCI Express ports) and I don't think it is generally safe to go and restore it early for every device (as explained in this changelog). > > In such cases the restoration of the device's config space will be > > retried during the "normal" phase of resume (ie. with interrupts > > enabled), so that the bridge can be put into D0 before that happens. > > If drivers have to assume it is restored late, anyway... why not do it > late, always? Because it breaks. Thanks, Rafael -- 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
