From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2034C2C15A8 for ; Tue, 28 Oct 2025 23:37:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761694643; cv=none; b=VWF3NtkuyYXbbNDJmkObSTvrZJwstMVunW/Y+KzYpDpJ+TB81YPQ4PnrJxigq8smWdLFfidqSF0iJAM9GpUFTfwsLNGRED+DwSoRkDBQH+TtXIIHIJZwvbRQ0JgD77HZX4ut28rD/aV9GNiSm8nA3xuY2guoJNBRKUZP5DsPSyA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761694643; c=relaxed/simple; bh=AWECh2OxHra3/PlA8PXFbZQ7bGQzWb8i9TX7i9CFy78=; h=From:To:Subject:Date:Message-ID:Content-Type:MIME-Version; b=djzEVIXoCunNYBNXP83dcFYhfYCQHl2ARx3PuY3pTPYM35407BBpJjGwZvkYp0Lj+G48m0bH3rdVkjy2fuUX66Mqzr88zOCy7n/y+HDSU8PSBpVnCjbUuhgQn/CbR4LGGHCrBn4OX7fIByKTbGYApBsdlvIf8e8XsRRfaYm9TWA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gKCngEWo; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gKCngEWo" Received: by smtp.kernel.org (Postfix) with ESMTPS id 9278FC4CEFD for ; Tue, 28 Oct 2025 23:37:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761694642; bh=AWECh2OxHra3/PlA8PXFbZQ7bGQzWb8i9TX7i9CFy78=; h=From:To:Subject:Date:From; b=gKCngEWoECxdflM5ZuhghoVSiQAIDdOYPoU5iDW3vbO6q2EvfEeeV4b+aGw+zyc54 +rj4qA43aIW8RBSE2LGt2YriWd7zMrxeAwH03VzNZD6wTwSJ/kmvjRqpvBOVIZgvSU OTQFNMuKwJ7xZqvS5cRxm2DZPtkjeggIiYx3PFwnNMUbzj4w4acpHsZjJbzOHx2pZX EGvcXXOCcrUG1D1uVOD3hFJc5NMVipdJ5n/+wxCmd/DCGdwAoHGC2hmhFNJ+V2uIsO aBnbG3rE0kOo24R/ibhx5xbe+2GM0h2ti9gy2N2pBYdsZ2oEEBnLU9FGJ7MN7Ivgbf g1XJ9pBvoDb2A== Received: by aws-us-west-2-korg-bugzilla-1.web.codeaurora.org (Postfix, from userid 48) id 88FB3C41613; Tue, 28 Oct 2025 23:37:22 +0000 (UTC) From: bugzilla-daemon@kernel.org To: linux-pm@vger.kernel.org Subject: [Bug 220715] New: [REGRESSION] AMD P-State fails with "_CPC object is not present" on AMD Zen 4 between 6.10 and 6.11 Date: Tue, 28 Oct 2025 23:37:22 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Power Management X-Bugzilla-Component: cpufreq X-Bugzilla-Version: 2.5 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: chris.harris79@gmail.com X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: linux-pm@vger.kernel.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version cf_kernel_version rep_platform op_sys bug_status bug_severity priority component assigned_to reporter cc cf_regression attachments.created Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugzilla.kernel.org/ Auto-Submitted: auto-generated Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 https://bugzilla.kernel.org/show_bug.cgi?id=3D220715 Bug ID: 220715 Summary: [REGRESSION] AMD P-State fails with "_CPC object is not present" on AMD Zen 4 between 6.10 and 6.11 Product: Power Management Version: 2.5 Kernel Version: 6.17.5 Hardware: AMD OS: Linux Status: NEW Severity: normal Priority: P3 Component: cpufreq Assignee: linux-pm@vger.kernel.org Reporter: chris.harris79@gmail.com CC: mario.limonciello@amd.com Regression: Yes Created attachment 308864 --> https://bugzilla.kernel.org/attachment.cgi?id=3D308864&action=3Dedit acpidump, dmesg with current kernel (6.17), dmesg with a last working kernel This bug was initially reported to linux-pm@vger.kernel.org and I was asked by Mario Limonciello to open this bugzilla and provide additional debug dat= a. SUMMARY ------- The AMD P-State driver fails to initialize on AMD Zen 4 processors starting with kernel 6.11.0, returning "_CPC object is not present in SBIOS or ACPI disabled" error. The same hardware works correctly with kernel 6.10.0 and earlier. The regression was introduced between 6.10.0 and 6.11.0. REGRESSION INFORMATION ---------------------- - Regression: Yes - Last working kernel: 6.10.14 - First broken kernel: 6.11.0 - Still broken in: 6.17.5, 6.18.0-rc3 ATTACHMENTS PROVIDED -------------------- 1. acpidump.txt - ACPI table dump (same across all kernels) 2. dmesg-6.10.14-061014-generic.txt - dmesg from WORKING kernel 3. dmesg-6.17.5-061705-generic.txt - dmesg from BROKEN kernel 4. system-info-6.10.14.txt - Additional system info from working kernel 5. system-info-6.17.5.txt - Additional system info from broken kernel tarball: amd-pstate-debug-all.tar.gz HARDWARE TESTED --------------- Reproduced on multiple AMD Zen 4 systems: System 1 (primary testing - multiple identical units tested): - CPU: AMD EPYC 4484PX 12-Core Processor - Motherboard: Supermicro H13SRE-F (Version 1.01) - System: Supermicro AS-3015MR-H10TNR - BIOS: American Megatrends International, LLC. v2.4 (04/29/2025, Revision 5.35) System 2 (additional confirmation): - CPU: AMD Ryzen 9 7950X 16-Core Processor - Motherboard: Supermicro H13SRD-F (Version 1.00) - System: Supermicro AS-3015MR-H8TNR - BIOS: American Megatrends International, LLC. v1.2a (07/10/2024, Revision 5.32) Both systems exhibit identical behavior with the regression. CPPC confirmed enabled in BIOS by vendor. Note: This issue likely affects all AMD Zen 4 processors and possibly other= AMD generations with CPPC support. REGRESSION TEST RESULTS ----------------------- Working (amd-pstate loads successfully): - 6.8.0-84-generic (Ubuntu 24.04) - 6.8.0-86-generic (Ubuntu 24.04) - 6.9.0-060900-generic (Ubuntu mainline) - 6.10.0-061000-generic (Ubuntu mainline) - 6.10.14-061014-generic (Ubuntu mainline) <- LAST WORKING (latest 6.10.x) Broken (falls back to acpi-cpufreq with _CPC error): - 6.11.0-061100-generic (Ubuntu mainline) <- FIRST BROKEN - 6.12.0-061200-generic (Ubuntu mainline) - 6.13.0-061300-generic (Ubuntu mainline) - 6.14.0-061400-generic (Ubuntu mainline) - 6.16.7-061607-generic (Ubuntu mainline) - 6.17.1-061701-generic (Ubuntu mainline) - 6.17.5-061705-generic (Ubuntu mainline) - 6.18.0-061800rc3-generic (Ubuntu mainline RC) - 6.17.1-1-cachyos-server-lto (Arch Linux) ERROR MESSAGE ------------- [ 4.508125] amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled STEPS TO REPRODUCE ------------------ 1. Boot with kernel parameter: amd_pstate=3Dpassive 2. Check driver: cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver Expected: amd-pstate Actual: acpi-cpufreq 3. Check dmesg: dmesg | grep "_CPC" Shows: "the _CPC object is not present in SBIOS or ACPI disabled" KERNEL CONFIGURATION -------------------- All tested kernels have identical AMD P-State configuration: CONFIG_ACPI_CPPC_LIB=3Dy CONFIG_X86_AMD_PSTATE=3Dy CONFIG_X86_AMD_PSTATE_DEFAULT_MODE=3D3 CONFIG_X86_AMD_PSTATE_UT=3Dm TESTING ENVIRONMENT ------------------- - Tested with vanilla kernels from Ubuntu mainline PPA - No additional modules or patches - Kernel not tainted - Reproduced on both Ubuntu 24.04 and Arch Linux distributions IMPACT ------ This regression prevents affected AMD systems from using the optimized AMD P-State driver, forcing fallback to generic acpi-cpufreq with approximately 5-10% performance loss for server and desktop workloads. Confirmed on both AMD EP= YC 4484PX and Ryzen 9 7950X (Zen 4), likely affecting all Zen 4 processors and possib= ly other AMD generations that support CPPC/ACPI P-States. BISECTION RESULTS ----------------- Through systematic testing of Ubuntu mainline kernels, I've identified the exact regression window: - Last working version: 6.10.14-061014-generic (all 6.10.x versions work) - First broken version: 6.11.0-061100-generic The regression was introduced during the 6.11 merge window. All 6.10.x vers= ions work correctly (tested 6.10.0 through 6.10.14), while all 6.11+ versions fa= il. The issue persists through all subsequent versions tested up to 6.18.0-rc3. The regression appears to be in ACPI _CPC object detection/parsing, as the = same BIOS/hardware combination works with the entire 6.10.x series but fails with 6.11+. ADDITIONAL INFORMATION ---------------------- The same ACPI tables and BIOS work correctly with 6.8, 6.9, and 6.10 kernel= s, confirming this is not a firmware issue but a kernel regression in CPPC/ACPI handling. >From working system (6.10.14): $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver amd-pstate - No error messages, driver loads successfully >From broken system (6.17.5): $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver acpi-cpufreq $ dmesg | grep amd_pstate [ 0.714133] amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled I've tested on multiple systems with identical results. I'm available for testing patches or providing additional debugging information as needed. I can perform git bisect between 6.10 and 6.11 if required to identify the specific commit that introduced this regression. Thank you for your attention to this regression. Chris Harris Keywords: amd-pstate cpufreq ACPI _CPC Zen4 --=20 You may reply to this email to add a comment. 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