From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7C2BACA5FA5 for ; Thu, 1 Oct 2026 09:01:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=TvwNQLjS611ibNT864zUTrO5ufiPUJUycmwdP21agp4=; b=cnPNbdh2kx76D5ocUGyqr+Qhe4 pD11EeINwLWVCyWXIBdMydeEG+RPSksDtr1MF4yG7bkN1BVqin60VUBHwuycNaB/uXG4pXbhVnKa9 yVundJDXl5gR/aa33qiEOw1jdUb/U2qBApdVCUSaXDAZdsSvJhLZ3PmdI39WWaePNPolHjB5nTbVi RG8ZqksUJe/QMin9gVPFJisqCNmX8HixZ6KX3Cp8iJEJdvIyXU1Vl5YV/frvdWVmsUrvkU95fmmIJ Lglby3CMPeHzpHF2nIjCWPqryKtMMKoD30oM/NVeQNQeDHblyYJtc56bOu1F8zVDIMnyuTBDqFbkB GeautekA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xCCf4-00000008IRd-43Sn; Thu, 01 Oct 2026 09:01:06 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xCCf2-00000008IQ9-3BfB for linux-arm-kernel@lists.infradead.org; Thu, 01 Oct 2026 09:01:06 +0000 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 E1678497; Thu, 1 Oct 2026 02:01:00 -0700 (PDT) Received: from e143943.arm.com (unknown [10.57.77.101]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id EF8233F85F; Thu, 1 Oct 2026 02:01:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790845264; bh=ToXKGxs2LrZ9zE0JvDN1qC6HPAAAfIqqEMJiKGlklWI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IJgZfc3y20b6S9dMZYFUZC3HV9hiTqOEcZjjS7eqqbzz5al4AUj/YKWu2TvbimICf P0L/lmVclDCo1wxxD7osws9VfYubqHV3rAJxNkdu1c+x9zdd+TS6Kyrg3ymbT+7oZd xLXuFsGbdMTxD4/VEosrJ2+zpu4v9OHFd5u1SUF8= 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 v4 2/2] arm64: errata: Add Cortex-A725 erratum 3821522 workaround Date: Thu, 1 Oct 2026 11:00:32 +0200 Message-ID: <20261001090050.3849551-3-beata.michalska@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261001090050.3849551-1-beata.michalska@arm.com> References: <20261001090050.3849551-1-beata.michalska@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261001_020104_928234_50ED057B X-CRM114-Status: GOOD ( 19.84 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 | 4 ++++ arch/arm64/kernel/topology.c | 9 +++++---- 4 files changed, 33 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 8ce559ac073c7..40c14e8600ae0 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -386,6 +386,10 @@ static const struct midr_range workaround_amu_constcnt_list[] = { #ifdef CONFIG_ARM64_ERRATUM_2457168 /* Cortex-A510 r0p0-r1p1 */ MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1), +#endif +#ifdef CONFIG_ARM64_ERRATUM_3821522 + /* Cortex-A725 r0p0 - r0p2 */ + 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..f1bdb49d5d92e 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 a HW erratum. + * 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