Hi Bjorn, Derrick,
On 5/22/20 12:46 PM, Bjorn Helgaas wrote:
On Fri, May 22, 2020 at 05:23:31PM +0000, Derrick, Jonathan wrote:
On Fri, 2020-05-01 at 11:35 -0600, Jonathan Derrick wrote:
On Fri, 2020-05-01 at 12:16 -0500, Bjorn Helgaas wrote:
On Thu, Apr 30, 2020 at 12:46:07PM -0600, Jon Derrick wrote:
Hi Bjorn & Kuppuswamy,
I see a problem in the DPC ECN [1] to _OSC in that it doesn't
give us a way to determine if firmware supports _OSC DPC
negotation, and therefore how to handle DPC.
Here is the wording of the ECN that implies that Firmware
without _OSC DPC negotiation support should have the OSPM rely
on _OSC AER negotiation when determining DPC control:
PCIe Base Specification suggests that Downstream Port
Containment may be controlled either by the Firmware or the
Operating System. It also suggests that the Firmware retain
ownership of Downstream Port Containment if it also owns
AER. When the Firmware owns Downstream Port Containment, it
is expected to use the new "Error Disconnect Recover"
notification to alert OSPM of a Downstream Port Containment
event.
In legacy platforms, as bits in _OSC are reserved prior to
implementation, ACPI Root Bus enumeration will mark these Host
Bridges as without Native DPC support, even though the
specification implies it's expected that AER _OSC negotiation
determines DPC control for these platforms. There seems to be
a need for a way to determine if the DPC control bit in _OSC
is supported and fallback on AER otherwise.
Currently portdrv assumes DPC control if the port has Native
AER services:
static int get_port_device_capability(struct pci_dev *dev)
...
if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
pci_aer_available() &&
(pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
services |= PCIE_PORT_SERVICE_DPC;
Newer firmware may not grant OSPM DPC control, if for
instance, it expects to use Error Disconnect Recovery. However
it looks like ACPI will use DPC services via the EDR driver,
without binding the full DPC port service driver.
If we change portdrv to probe based on host->native_dpc and
not AER, then we break instances with legacy firmware where
OSPM will clear host->native_dpc solely due to _OSC bits being
reserved:
struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
...
if (!(root->osc_control_set & OSC_PCI_EXPRESS_DPC_CONTROL))
host_bridge->native_dpc = 0;
So my assumption instead is that host->native_dpc can be 0 and
expect Native DPC services if AER is used. In other words, if
and only if DPC probe is invoked from portdrv, then it needs
to rely on the AER dependency. Otherwise it should be assumed
that ACPI set up DPC via EDR. This covers legacy firmware.
However it seems like that could be trouble with newer
firmware that might give OSPM control of AER but not DPC, and
would result in both Native DPC and EDR being in effect.
Anyways here are two patches that give control of AER and DPC
on the results of _OSC. They don't mess with the HEST parser
as I expect those to be removed at some point. I need these
for VMD support which doesn't even rely on _OSC, but I suspect
this won't be the last effort as we detangle Firmware First.
[1] https://members.pcisig.com/wg/PCI-SIG/document/12888
Hi Jon, I think we need to sort out the _OSC/FIRMWARE_FIRST patches
from Alex and Sathy first, then see what needs to be done on top of
those, so I'm going to push these off for a few days and they'll
probably need a refresh.
Bjorn
Agreed, no need to merge now. Just wanted to bring up the DPC
ambiguity, which I think was first addressed by dpc-native:
commit 35a0b2378c199d4f26e458b2ca38ea56aaf2d9b8
Author: Olof Johansson <olof@xxxxxxxxx>
Date: Wed Oct 23 12:22:05 2019 -0700
PCI/DPC: Add "pcie_ports=dpc-native" to allow DPC without AER control
Prior to eed85ff4c0da7 ("PCI/DPC: Enable DPC only if AER is available"),
Linux handled DPC events regardless of whether firmware had granted it
ownership of AER or DPC, e.g., via _OSC.
PCIe r5.0, sec 6.2.10, recommends that the OS link control of DPC to
control of AER, so after eed85ff4c0da7, Linux handles DPC events only if it
has control of AER.
On platforms that do not grant OS control of AER via _OSC, Linux DPC
handling worked before eed85ff4c0da7 but not after.
To make Linux DPC handling work on those platforms the same way they did
before, add a "pcie_ports=dpc-native" kernel parameter that makes Linux
handle DPC events regardless of whether it has control of AER.
[bhelgaas: commit log, move pcie_ports_dpc_native to drivers/pci/]
Link: https://lore.kernel.org/r/20191023192205.97024-1-olof@xxxxxxxxx
Signed-off-by: Olof Johansson <olof@xxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Are you still thinking about removing the HEST parser?
For VMD we still need the ability to bind DPC if native_dpc==1.
I think if we can do that, this set should still pretty much still
apply with a modification to patch 2 to allow matching
pcie_ports_dpc_native in dpc_probe.
Yes, I think we should remove the HEST firmware-first parsing, because
IIRC the spec really doesn't specify any action the OS should take
based on it. I was thinking Sathy might update the patch, and it fell
off my radar.
Sorry for the delay.
I was just waiting to see whether we get any issues with merging
following commit.
commit c100beb9ccfb98e2474586a4006483cbf770c823
Author: Alexandru Gagniuc <mr.nuke.me@xxxxxxxxx>
Date: Mon Apr 27 18:25:13 2020 -0500
PCI/AER: Use only _OSC to determine AER ownership
Since I did not see any email reporting any issues about it,
I will work on follow up patch.
Bjorn
