在 2023/4/13 0:32, Bjorn Helgaas 写道:
On Wed, Apr 12, 2023 at 05:11:28PM +0800, LeoLiuoc wrote:
在 2023/4/8 7:18, Bjorn Helgaas 写道:
On Tue, Nov 15, 2022 at 11:11:15AM +0800, LeoLiu-oc wrote:
From: leoliu-oc <leoliu-oc@xxxxxxxxxxx>
According to the sec 18.3.2.4, 18.3.2.5 and 18.3.2.6 in ACPI r6.5, the
register values form HEST PCI Express AER Structure should be written to
relevant PCIe Device's AER Capabilities. So the purpose of the patch set
is to extract register values from HEST PCI Express AER structures and
program them into AER Capabilities. Refer to the ACPI Spec r6.5 for a more
detailed description.
I wasn't involved in this part of the ACPI spec, and I don't
understand how this is intended to work.
I see that this series extracts AER mask, severity, and control
information from the ACPI HEST table and uses it to configure PCIe
devices as they are enumerated.
What I don't understand is how this relates to ownership of the AER
capability as negotiated by the _OSC method. Firmware can configure
the AER capability itself, and if it retains control of the AER
capability, the OS can't write to it (with the exception of clearing
EDR error status), so this wouldn't be necessary.
There is no relationship between the ownership of the AER related
register and the ownership of the AER capability in the OS or
Firmware.
I don't understand this; can you say it another way? "Ownership of
the AER related register" and "ownership of the AER capability" sound
exactly the same to me.
I would like to state that the operation of writing the AER capability
register of the relevant PCIe device through the HEST PCI Express AER
structure has nothing to do with the ownership of the AER.
I do not find a direct statement from ACPI Spec r6.5 that allows the OS
to write the value of the HEST AER register to the AER register of the
corresponding device without AER control but I looked in ACPI Spec for a
description of the relationship between writing to the AER register
through the _HPP/_HPX method and whether the OS requires AER control：
The expression are as follows:
1. OSPM uses the information returned by _HPX to determine how ①to
configure PCI Functions that are hot- plugged into the system, ②to
configure Functions not configured by the platform firmware during
initial system boot, ③and to configure Functions any time they lose
configuration space settings (e.g. OSPM issues a Secondary Bus
Reset/Function Level Reset or Downstream Port Containment is triggered).
2. _HPX may return multiple types or Record Settings (each setting in a
single sub-package.) OSPM is responsible for detecting the type of
Function and for applying the appropriate settings. OSPM is also
responsible for detecting the device / port type of the PCI Express
Function and applying the appropriate settings provided. For example,
the Secondary Uncorrectable Error Severity and Secondary Uncorrectable
Error Mask settings of Type 2 record are only applicable to PCI Express
to PCI-X/PCI Bridge whose device / port type is 1000b. Similarly, AER
settings are only applicable to hot plug PCI Express devices that
support the optional AER capability.
3. Note: OSPM may override the settings provided by the _HPX object’s
Type2 record (PCI Express Settings) or Type3 record (PCI Express
Descriptor Settings) when OSPM has assumed native control of the
corresponding feature. For example, if OSPM has assumed ownership of AER
(via _OSC), OSPM may override AER related settings returned by _HPX.
This means that writing the AER register value by _HPX does not require
the OS to gain control of the AER. Also from the usage description of
_HPX, I think ownership of AER means who decides the configuration value
of the AER register rather than who can write the configuration value.
Even though the OS does not have control or ownership of the AER, it
should still write the configuration values determined by the firmware
to the AER register at the request of the firmware. Therefore,
considering that HEST AER patch is an effective supplement to _HPP/_HPX
method when the Firmware does not support the _HPP/_HPX method, I think
the question about whether OS has control of AER to write the
information in the HEST AER structure to the AER register of the
corresponding device is similar to the question about _HPX/_HPP method
to write the AER information to the AER register of the corresponding
device. Therefore, the ownership of AER is not considered in this patch.
The processing here is to initialize the AER related register, not
the AER event. If Firmware is configured with AER register, it will
not be able to handle the runtime hot reset and link retrain cases
in addition to the hotplug case you mentioned below.
If the OS owns the AER capability, I assume it gets to decide for
itself how to configure AER, no matter what the ACPI HEST says.
What information does the OS use to decide how to configure AER? The
ACPI Spec has the following description: PCI Express (PCIe) root
ports may implement PCIe Advanced Error Reporting (AER) support.
This table(HEST) contains information platform firmware supplies to
OSPM for configuring AER support on a given root port. We understand
that HEST stands for user to express expectations.
In the current implementation, the OS already configures a PCIE
device based on _HPP/_HPX method when configuring a PCI device
inserted into a hot-plug slot or initial configuration of a PCI
device at system boot. HEST is just another way to express the
desired configuration of the user.
Why was the HEST mechanism added if the functionality is equivalent
to the existing _HPP/_HPX? There must be something that HEST supplies
that _HPP/_HPX did not.
I think we need some things in the commit log (and short comments in
the code) to help maintain this in the future:
- What problem does this solve, e.g., is there some bug that happens
because we lack this functionality?
- How is this HEST mechanism related to _HPP/_HPX? What are the
differences?
- How is this related to _OSC AER ownership?
Yes, I'll add explanations of these issues to the commit log in the next
release.
I think we ignore _OSC ownership in the existing _HPP/_HPX code, but
that seems like a potential problem. The PCI Firmware spec (r3.3, sec
4.5.1) is pretty clear:
If control of this feature was requested and denied or was not
requested, firmware returns this bit set to 0, and the operating
system must not modify the Advanced Error Reporting Capability or
the other error enable/status bits listed above.
PCI Firmware Spec is not very clear about the relationship between
configuring the AER register and the ownership of the AER. ACPI Spec
v6.5 does specify the use of _HPP or _HPX: writing to the AER register
through the _HPP/HPX method does not require the OS to acquire control
of the AER.
Your Sincerely,
LeoLiu-oc
Maybe this is intended for the case where firmware retains AER
ownership but the OS uses native hotplug (pciehp), and this is a way
for the OS to configure new devices as the firmware expects? But in
that case, we still have the problem that the OS can't write to the
AER capability to do this configuration.
Bjorn
