From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AB49C3E4C99 for ; Tue, 29 Sep 2026 15:43:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790696633; cv=none; b=SPamtR/AjWYI+AbYjKo/1cuPpelgpgoZ6rq0sCOO3cTh1IUS6t6h2WjYNDqhlT0dmDo++q2BfObJlfVGPYJj3SMtOp+BPI4aPnfLC8hCKCoHPFPxqHUr5Uumdq8PFrMK8jLlpIAKvBQb3lbWpYn21xS4hyWNAQBPC6ZdCg5f9os= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790696633; c=relaxed/simple; bh=V/tUooPNlebKcQB0HknU/9mJx7YkJKUKQx5qRAkTRsE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jTyHY2lI5gBoWbQKeHOk1HhmJ5a0QFQqjB98Cr7lQy7TmpsmfEX125h5K0KEAnK8mLWQw94ADF3dtkmYRmnfDSY8BXASIdWMTWIaC2SeL2GptDD7WIcJatGQja9mXVp087stlvEVsxGwlCsMCh8jxsejjVHy1JFV57lSwONOvwY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=DD0JKSfp; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="DD0JKSfp" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A82481516; Tue, 29 Sep 2026 08:43:47 -0700 (PDT) Received: from e143943.arm.com (unknown [10.57.78.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id D80B03F85F; Tue, 29 Sep 2026 08:43:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790696631; bh=V/tUooPNlebKcQB0HknU/9mJx7YkJKUKQx5qRAkTRsE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DD0JKSfpn7iabmL+BkiZLW31oyx5g+T5wmiBffwyNZGg1h6zOHPNC5MxmAN1s4YQW XnxEPeMQUB9VO6avh5V6UuL4GVzM/ebUfVOXTAPQ/3yo6TGLCCSstOG2lZqGKGK/Uu wI+2oUXtQqI16EQSm87Zp93uuHwQe4BAMZ5mWLjM= From: Beata Michalska To: linux-arm-kernel@lists.infradead.org Cc: Vladimir.Murzin@arm.com, catalin.marinas@arm.com, will@kernel.org, suzuki.poulose@arm.com, James.Morse@arm.com, xuewen.yan94@gmail.com, seanwang1@lenovo.com, linux-kernel@vger.kernel.org Subject: [PATCH v3 2/2] arm64: errata: Add Cortex-A725 erratum 3821522 workaround Date: Tue, 29 Sep 2026 17:42:14 +0200 Message-ID: <20260929154325.3416271-3-beata.michalska@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260929154325.3416271-1-beata.michalska@arm.com> References: <20260929154325.3416271-1-beata.michalska@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Cortex-A725 erratum 3821522 affects the CNT_CYCLES event, which can incur a significant increment error when a CPU enters and subsequently exits WFE or WFI, and may no longer track the system counter frequency. The AMEVCNTR01_EL0 counter is used as the AMU constant counter for frequency invariance and CPPC FFH feedback counters. Wire the affected Cortex-A725 range into the shared broken AMU constant-counter capability so the affected counter is treated as unavailable by returning zero in the AMU counter paths. This prevents the broken counter from being used as a reference source. The erratum can also affect PMUv3 users of the CNT_CYCLES event, but this workaround intentionally does not change PMU event handling. Hiding or rejecting the PMU event from the erratum code would change the perf-visible PMU event interface, including raw event selection, and would need a separate PMU-specific approach rather than being folded into the AMU reference-counter workaround. Cc: Signed-off-by: Beata Michalska --- Documentation/arch/arm64/silicon-errata.rst | 2 ++ arch/arm64/Kconfig | 22 +++++++++++++++++++++ arch/arm64/kernel/cpu_errata.c | 6 ++++++ arch/arm64/kernel/topology.c | 9 +++++---- 4 files changed, 35 insertions(+), 4 deletions(-) diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst index ac3248b9f2f3b..99a1eb4b833dd 100644 --- a/Documentation/arch/arm64/silicon-errata.rst +++ b/Documentation/arch/arm64/silicon-errata.rst @@ -174,6 +174,8 @@ stable kernels. +----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-A725 | #3456106 | ARM64_ERRATUM_3194386 | +----------------+-----------------+-----------------+-----------------------------+ +| ARM | Cortex-A725 | #3821522 | ARM64_ERRATUM_3821522 | ++----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-X1 | #1502854 | N/A | +----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-X1 | #3324344 | ARM64_ERRATUM_3194386 | diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 3b6c052d46a18..cab741a695f52 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1081,6 +1081,28 @@ config ARM64_ERRATUM_2645198 If unsure, say Y. +config ARM64_ERRATUM_3821522 + bool "Cortex-A725: 3821522: workaround for possible CNT_CYCLES increment error due to WFE/WFI" + depends on ARM64_AMU_EXTN + select ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT + default y + help + This option adds the workaround for ARM Cortex-A725 erratum 3821522. + + On affected A725 cores, the CNT_CYCLES event may incur a significant + increment error when entering and subsequently exiting WFx. + As a result, the CNT_CYCLES may diverge from the system counter + frequency at which it is expected to increment. + This renders the AMU counter AMEVCNTR01, that implements CNT_CYCLES, + being unreliable and unsuitable for use. + + Since there is no hardware workaround, reads of the affected CNT_CYCLES + counter return 0 in the relevant paths. This causes users of the counter + to treat it as unavailable and is functionally equivalent to firmware + disabling the affected counter. + + If unsure, say Y. + config ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD bool diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index f18683e56184b..42a6fff8c3f44 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -388,6 +388,12 @@ static const struct arm64_cpu_capabilities arm64_repeat_amu_constcnt_list[] = { /* Cortex-A510 r0p0-r1p1 */ CAP_MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1) }, +#endif +#ifdef CONFIG_ARM64_ERRATUM_3821522 + { + /* Cortex-A725 r0p0 - r0p2 */ + CAP_MIDR_RANGE(MIDR_CORTEX_A725, 0, 0, 0, 2) + }, #endif {} }; diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index 64588554e7f76..fc5d3abd12905 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -397,10 +397,11 @@ static void cpu_read_corecnt(void *val) static void cpu_read_constcnt(void *val) { /* - * Return 0 if the current CPU is affected by erratum 2457168. A value - * of 0 is also returned if the current CPU does not support AMUs or if - * the counter is disabled. A return value of 0 at counter read is - * properly handled as an error case by the users of the counter. + * Return 0 if the current CPU is affected by either erratum 2457168 + * or erratum 3821522. A value of 0 is also returned if the current + * CPU does not support AMUs or if the counter is disabled. A return + * value of 0 at counter read is properly handled as an error case + * by the users of the counter. */ *(u64 *)val = this_cpu_has_cap(ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT) ? 0UL : read_constcnt(); -- 2.43.0