On 6/6/2023 2:58 PM, Bjorn Helgaas wrote:
On Tue, Jun 06, 2023 at 02:40:45PM -0500, Limonciello, Mario wrote:
On 6/6/2023 2:23 PM, Bjorn Helgaas wrote:
On Tue, Jun 06, 2023 at 11:23:21AM -0500, Mario Limonciello wrote:
ASMedia PCIe GPIO controllers fail functional tests after returning from
suspend (S3 or s2idle). This is because the BIOS checks whether the
OSPM has called the `_REG` method to determine whether it can interact with
the OperationRegion assigned to the device.
As described in 6.5.4 in the APCI spec, `_REG` is used to inform the AML
code on the availability of an operation region.
To fix this issue, call acpi_evaluate_reg() when saving and restoring the
state of PCI devices.
Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/06_Device_Configuration/Device_Configuration.html#reg-region
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
v1->v2:
* Handle case of no CONFIG_ACPI
* Rename function
* Update commit message
* Move ACPI calling code into pci-acpi.c instead
* Cite the ACPI spec
Thanks for the spec reference (s/APCI/ACPI/ and add the revision if
you rev this (r6.5 is the latest, AFAIK) if you rev this).
I don't see text in that section that connects S3 with _REG. If it's
there, you might have to quote the relevant sentence or two in the
commit log.
I don't think there is anything the spec connecting this
with S3. At least from my perspective S3 is the reason
this was exposed but there is a deficiency that exists
that _REG is not being called by Linux.
I intend to re-word the commit message something to the
effect of explaining what _REG does and why _REG should be
called, along with citations.
Then in another paragraph "Fixing this resolves an issue ...".
You mentioned _REG being sort of a mutex to synchronize OSPM vs
platform access; if there's spec language to that effect, let's cite
it.
That sentence I included was cited from the spec.
If it's necessary to justify the commit, include the citation in the
commit log.
Ideally we should have been able to read the PCI and ACPI specs and
implement this without tripping over problem on this particular
hardware. I'm looking for the text that enables that "clean-room"
implementation. If the spec doesn't have that text, it's either a
hole in the spec or a BIOS defect that depends on something the spec
doesn't require.
IMO both the spec and BIOS are correct, it's a Linux
issue that _REG wasn't used.
What tells Linux that _REG needs to be used here? If there's nothing
that tells Linux to use _REG here, I claim it's a BIOS defect. I'm
happy to be convinced otherwise; the way to convince me is to point to
the spec.
From the spec it says "control methods must assume
all operation regions are inaccessible until the
_REG(RegionSpace, 1) method is executed"
It also points out the opposite: "Conversely,
control methods must not access fields in
operation regions when _REG method execution
has not indicated that the operation region
handler is ready."
The ACPI spec doesn't refer to D3 in this context, but
it does make an allusion to power off in an example case.
"Also, when the host controller or bridge controller
is turned off or disabled, PCI Config Space Operation
Regions for child devices are no longer available.
As such, ETH0’s _REG method will be run when it is
turned off and will again be run when PCI1 is
turned off."
If it's a BIOS defect, it's fine to work around it, but we need to
understand that, own up to it, and make the exact requirements very
clear. Otherwise we're likely to break this in the future because
future developers and maintainers will rely on the specs.
From my discussions with BIOS developers, this is entirely
intended behavior based on the _REG section in the spec.
Doing this in pci_save_state() still seems wrong to me. For example,
e1000_probe() calls pci_save_state(), but this is not part of suspend.
IIUC, this patch will disconnect the opregion when we probe an e1000
NIC. Is that what you intend?
Thanks for pointing this one out. I was narrowly focused
on callers in PCI core. This was a caller I wasn't
aware of; I agree it doesn't make sense.
I think pci_set_power_state() might be another good
candidate to use. What do you think of this?
I can't suggest a call site because (1) I'm not a power management
person, and (2) I don't think we have a clear statement of when it is
required. This must be expressed in terms of PCI power state
transitions, or at least something discoverable from a pci_dev, not
"s2idle" or even "S3" because those are meaningless in the PCI
context.
Bjorn
Right; I'm with you on not putting it with a suspend
transition.
The spec indicates that control methods can't access
the regions until _REG is called, so
my leaning is to keep the call at init time, and
then add another call for the D3 and D0 transitions
which is why I think pci_set_power_state() is probably
best.
