Messages in this thread | | | Subject | Re: [PATCH v3 0/2] PCI/ERR: Allow Native AER/DPC using _OSC | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Fri, 22 May 2020 13:48:12 -0700 |
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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@lixom.net> >>> 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@lixom.net >>> Signed-off-by: Olof Johansson <olof@lixom.net> >>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> >> >> 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@gmail.com> 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 >
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