On Tue, Apr 5, 2022 at 1:45 PM Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> wrote: > > Hi Rafael, > > On Mon, Apr 04, 2022 at 05:20:30PM +0200, Rafael J. Wysocki wrote: > > Hi All, > > > > There are cases in which the power state of a PCI device depends on an ACPI > > power resource (or more of them) in such a way that when the given power > > resource is in the "off" state, the PCI device depending on it is in D3cold. > > > > On some systems, the initial state of these power resources is "off", so the > > kernel should not access the config space of PCI devices depending on them, > > until the power resources in question are turned "on", but currently that is > > not respected during PCI device enumeration. Namely, the PCI device > > enumeration code walks the entire bus and enumerates all of the devices it > > can find, including the ones whose initial power state in principle depends on > > the ACPI power resources in the "off" state. > > I guess these devices do not have _PRE() method either. Personally, I haven't seen any ACPI tables containing any _PRE yet. > > Apparently, most of the time, the config space of such devices is accessible > > regardless of the state of the ACPI power resource associated with the PCI > > device, so the device enumeration is successful, but there are two potential > > issues related to this behavior. First off, even if the given PCI device > > is accessible when the ACPI power resource depended on by it is "off", > > changing its configuration may confuse the platform firmware and lead to > > problems when the ACPI power resource in question is turned "on". Second, > > the PCI device may not be actually accessible at all when the ACPI power > > resource depended on by it is "off", in which case it won't be found during > > the PCI enumeration of devices. > > > > This patch series addresses that problem by turning "on" all ACPI power > > resources depended on by PCI devices before attempting to access the config > > space of those devices for the first time. > > Makes sense. > > For the series, > > Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> Thanks!
