Hi,,,I am investigating a reproducible Bluetooth SAR initialization warning on an Intel AX201 controller in an ASUS ExpertBook B5402CBA running Gentoo Linux.,,The warning occurs during firmware initialization on both Linux 7.3.3 and 7.3.4:,,```,Bluetooth: hci0: Applying legacy Bluetooth SAR,Bluetooth: hci0: Failed to send sar ddc id:0x0137 (-22),```,,I captured the initial firmware initialization with btmon and confirmed that the controller explicitly rejects Intel DDC Config Write (0xfc8b), ID 0x0137, with HCI status 0x12.,,**Environment**,,- Hardware: Intel AX201 (USB 8087:0026),- Laptop: ASUS ExpertBook B5402CBA,- Kernel: Gentoo Linux 7.3.4-bdsm (also observed on 7.3.3-bdsm),- Bluetooth firmware: 2026.29, build 82200,- Firmware SHA1 reported by controller: 0xd3d4fa22,- CNVi TOP: 0x00080400,- CNVr TOP: 0x01300504,- Intel DDC file: intel/ibt-0040-4150.ddc (symlink to ibt-0040-0041.ddc),,**Confirmed HCI sequence**,,```,DDC ID Payload HCI status,0x0128 18 Success (0x00),0x0129 03 00 Success (0x00),0x0131 06 Success (0x00),0x0132 06 Success (0x00),0x0133 07 Success (0x00),0x0137 06 08 08 Invalid HCI Command Parameters (0x12),```,,The initial DDC configuration file contains only IDs 0x0128 and 0x0129, and both are applied successfully.,,The legacy SAR parameters come from the ACPI BRDS method at:,,```,\_SB.PC00.XHCI.RHUB.HS10,```,,The method reads the Bluetooth SAR values from the ASUS GNVS SystemMemory region. The controller initialization takes the legacy SAR path.,,In `btintel_set_legacy_sar()`, the first three SAR commands succeed. The next command, ID 0x0137 with payload `06 08 08`, is rejected. The function then returns without sending the remaining legacy SAR commands.,,**Questions**,,1. Is legacy SAR DDC ID 0x0137 with a three-byte BR/EDR payload expected to be supported by this AX201 firmware and hardware generation?,2. Are the payload values `06 08 08` valid for this command, or could the rejection indicate incompatible ACPI-provided SAR values?,3. If this rejection is expected for some Intel controllers, should `btintel` check capability or handle the unsupported command differently, while preserving the required radio power restrictions?,4. Could this result in only partial application of the platform's Bluetooth SAR settings?,,The controller finishes initialization and Bluetooth remains usable. I am not claiming that this warning causes the separate intermittent hardware error 0x0c observed on the system.,,I can provide a sanitized btmon capture, relevant DSDT/BRDS excerpts, and kernel initialization logs if useful.,,Thanks for looking into this.

[Vovan Nikolaevich <vov4ik533@gmail.com>]

Hi,

I am investigating a reproducible Bluetooth SAR initialization warning 
on an Intel AX201 controller in an ASUS ExpertBook B5402CBA running 
Gentoo Linux.

The warning occurs during firmware initialization on both Linux 7.3.3 
and 7.3.4:

Bluetooth: hci0: Applying legacy Bluetooth SAR
Bluetooth: hci0: Failed to send sar ddc id:0x0137 (-22)

I captured the initial firmware initialization with btmon and confirmed 
that the controller explicitly rejects Intel DDC Config Write (0xfc8b), 
ID 0x0137, with HCI status 0x12.

Environment

Hardware: Intel AX201 (USB 8087:0026)

Laptop: ASUS ExpertBook B5402CBA

Kernel: Gentoo Linux 7.3.4-bdsm (also observed on 7.3.3-bdsm)

Bluetooth firmware: 2026.29, build 82200

Firmware SHA1 reported by controller: 0xd3d4fa22

CNVi TOP: 0x00080400

CNVr TOP: 0x01300504

Intel DDC file: intel/ibt-0040-4150.ddc (symlink to ibt-0040-0041.ddc)

Confirmed HCI sequence

DDC ID   Payload    HCI status
0x0128   18         Success (0x00)
0x0129   03 00      Success (0x00)
0x0131   06         Success (0x00)
0x0132   06         Success (0x00)
0x0133   07         Success (0x00)
0x0137   06 08 08   Invalid HCI Command Parameters (0x12)

The initial DDC configuration file contains only IDs 0x0128 and 0x0129, 
and both are applied successfully.

The legacy SAR parameters come from the ACPI BRDS method at:

\_SB.PC00.XHCI.RHUB.HS10

The method reads the Bluetooth SAR values from the ASUS GNVS 
SystemMemory region. The controller initialization takes the legacy SAR 
path.

In btintel_set_legacy_sar(), the first three SAR commands succeed. The 
next command, ID 0x0137 with payload 06 08 08, is rejected. The function 
then returns without sending the remaining legacy SAR commands.

Questions

Is legacy SAR DDC ID 0x0137 with a three-byte BR/EDR payload expected to 
be supported by this AX201 firmware and hardware generation?

Are the payload values 06 08 08 valid for this command, or could the 
rejection indicate incompatible ACPI-provided SAR values?

If this rejection is expected for some Intel controllers, should btintel 
check capability or handle the unsupported command differently, while 
preserving the required radio power restrictions?

Could this result in only partial application of the platform's 
Bluetooth SAR settings?

The controller finishes initialization and Bluetooth remains usable. I 
am not claiming that this warning causes the separate intermittent 
hardware error 0x0c observed on the system.

I can provide a sanitized btmon capture, relevant DSDT/BRDS excerpts, 
and kernel initialization logs if useful.

Thanks for looking into this.