[+cc Rafael, linux-acpi] On Mon, Apr 02, 2018 at 05:09:49PM -0600, Keith Busch wrote: > On Mon, Apr 02, 2018 at 04:23:02PM -0500, Bjorn Helgaas wrote: > > On Mon, Apr 02, 2018 at 10:21:57AM -0600, Keith Busch wrote: > > > A DPC port may be configured to send ERR_COR message when the > > > triggered. This patch enables this feature so additional notification > > > of the event is possible. > > > > Who is the intended consumer of the ERR_COR message? I guess if the > > root port supports AER, we'll see AER logging when we didn't before? > > Is that what you mean by "additional notification"? > > > > Or, since the DPC ERR_COR implementation note (sec 6.2.10.2) suggests > > that ERR_COR is primarily intended for use by platform firmware, does > > this change enable notification via the firmware? If so, how does > > that work? Does it require the platform to retain control of AER so > > it can see these events? But if the platform retains AER control, I > > don't think we'd be enabling DPC in Linux. I'm confused. > > > > The similar implementation note in 6.2.10.5 suggests that > > DL_ACTIVE_ERR_COR is also intended for use by the platform. Should we > > be setting that for the same reason we're setting > > PCI_EXP_DPC_CTL_ERR_COR? > > I think there are various ways this could play out. I added this to > the series per a request for future use, but I actually don't have an > environment where I could test as intended. As I understand, it was > for platform firmware that may own the root port, but not switches in > an external enclosure, so the OS would own the DPC control. The ERR_COR > is to notify firmware so it may note an event in a platform log. This picture doesn't make sense to me yet. Per the PCI Firmware spec, r3.2, sec 4.5.2, we use _OSC to negotiate control over AER (and now DPC). I think _OSC is only allowed directly under a host bridge device (PNP0A08 or PNP0A03), and it applies to the entire hierarchy under the host bridge. I don't know how firmware could claim to own AER on a root port, but not on switches (external or otherwise) below that root port. If _OSC says firmware owns AER, we won't touch AER on the root port, but we also won't touch DPC on switches below the root port. So I don't see how this change will help. > I think you bring up a good point on DL_Active. > > This should be harmless even if there are no consumers for the message, > or if the OS owns the root port AER control. But I'm totally fine > with dropping this one in the series, and it's not related to the rest > anyway. I think I at least need to circle back with platform makers and > really test the feature on capable hardware.
