[PATCH] ACPI: PCI: Avoid misleading _OSC messages for non-PCIe host bridges without _OSC

[PATCH] ACPI: PCI: Avoid misleading _OSC messages for non-PCIe host bridges without _OSC

[KONDO KAZUMA(近藤 和真)]

After commit 7d703df7f4f5 ("ACPI: bus: Split _OSC evaluation out of
acpi_run_osc()"), the _OSC evaluation path now returns AE_ERROR to
negotiate_os_control() instead of propagating AE_NOT_FOUND from
acpi_evaluate_object().

This has not caused any functional issues so far, but it produces
additional misleading messages for non-PCIe host bridges without _OSC on
some Intel servers:

    kernel: ACPI: Enabled 2 GPEs in block 00 to 7F
    kernel: ACPI: PCI Root Bridge [UNC0] (domain 0000 [bus fe])
    kernel: acpi PNP0A03:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM Segments MSI EDR HPX-Type3]
  + kernel: acpi PNP0A03:00: _OSC: OS requested [PCIeHotplug SHPCHotplug PME AER PCIeCapability LTR DPC]
  + kernel: acpi PNP0A03:00: _OSC: platform willing to grant [PCIeHotplug SHPCHotplug PME AER PCIeCapability LTR DPC]
  + kernel: acpi PNP0A03:00: _OSC: platform retains control of PCIe features (AE_ERROR)
    kernel: PCI host bridge to bus 0000:fe

Previously, negotiate_os_control() silently ignored AE_NOT_FOUND for
non-PCIe host bridges without _OSC, but after the above change, it no
longer does so.

As a result, negotiate_os_control() logs messages as if the OS had
negotiated with the platform via _OSC, even though the non-PCIe host
bridge has no _OSC method and no such negotiation actually occurs.

Skip _OSC negotiation for non-PCIe host bridges that do not define an
_OSC method before attempting to evaluate it.

Fixes: 7d703df7f4f5 ("ACPI: bus: Split _OSC evaluation out of acpi_run_osc()")
Link: https://lore.kernel.org/linux-acpi/d0be949d-0e21-472e-a44b-cedb1dd8695d@nec.com/
Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Kazuma Kondo <kazuma-kondo@nec.com>
---
 drivers/acpi/pci_root.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 4c06c3ffd0cb..3a24d018436b 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -574,6 +574,12 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
 		return;
 	}
 
+	/* _OSC is optional for PCI host bridges */
+	if (!is_pcie(root) && !acpi_has_method(handle, "_OSC")) {
+		dev_dbg(&device->dev, "_OSC: negotiation skipped (method not present for non-PCIe host bridge)\n");
+		return;
+	}
+
 	support = calculate_support();
 
 	decode_osc_support(root, "OS supports", support);
@@ -615,10 +621,6 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
 		 */
 		*no_aspm = 1;
 
-		/* _OSC is optional for PCI host bridges */
-		if (status == AE_NOT_FOUND && !is_pcie(root))
-			return;
-
 		if (control) {
 			decode_osc_control(root, "OS requested", requested);
 			decode_osc_control(root, "platform willing to grant", control);
-- 
2.49.0

Re: [PATCH] ACPI: PCI: Avoid misleading _OSC messages for non-PCIe host bridges without _OSC

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Early return bypasses ASPM disablement for non-PCIe and CXL host bridges without _OSC, causing an undocumented functional change and potential instability
--

--- Patch [1]: [PATCH] ACPI: PCI: Avoid misleading _OSC messages for non-PCIe host bridges without _OSC ---
commit e68d29f653a1c34f8b7b08baaa548e2ff2d3663f
Author: KONDO KAZUMA( $B6aF#!!OB?? (B) <kazuma-kondo@nec.com>

ACPI: PCI: Avoid misleading _OSC messages for non-PCIe host bridges without _OSC

This patch skips _OSC negotiation for non-PCIe host bridges that do not define
an _OSC method before attempting to evaluate it. It aims to prevent misleading
messages in the logs on some Intel servers where the OS appears to negotiate
with the platform despite the lack of an _OSC method.

Link: https://lore.kernel.org/linux-acpi/d0be949d-0e21-472e-a44b-cedb1dd8695d@nec.com/

> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 4c06c3ffd0cbb..3a24d018436b4 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -574,6 +574,12 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
>  		return;
>  	}
>  
> +	/* _OSC is optional for PCI host bridges */
> +	if (!is_pcie(root) && !acpi_has_method(handle, "_OSC")) {
> +		dev_dbg(&device->dev, "_OSC: negotiation skipped (method not present for non-PCIe host bridge)\n");
> +		return;
> +	}
> +

[Severity: High]
Does this early return unintentionally skip disabling ASPM for these host
bridges?

The commit message states this change produces no functional issues and only
removes misleading messages. However, before this patch, if the _OSC method
was missing, the function would proceed, fail the negotiation, and fall
through to the failure path where *no_aspm = 1 is unconditionally set.

By returning early here, it looks like *no_aspm = 1 is completely bypassed
for legacy host bridges.

Additionally, is_pcie() only checks for ACPI_BRIDGE_TYPE_PCIE. Could this
cause CXL host bridges (ACPI_BRIDGE_TYPE_CXL) to evaluate to false here?
If a CXL bridge lacks an _OSC method, it would take this early return and skip
ASPM disablement entirely, which could leave ASPM enabled inappropriately
without firmware negotiation.

>  	support = calculate_support();
>  
>  	decode_osc_support(root, "OS supports", support);

[ ... ]

> @@ -615,10 +621,6 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
>  		 */
>  		*no_aspm = 1;
>  
> -		/* _OSC is optional for PCI host bridges */
> -		if (status == AE_NOT_FOUND && !is_pcie(root))
> -			return;
> -
>  		if (control) {
>  			decode_osc_control(root, "OS requested", requested);
>  			decode_osc_control(root, "platform willing to grant", control);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260731090820.493064-1-kazuma-kondo@nec.com?part=1