linux-kernel - [PATCH AUTOSEL 6.6 09/23] iommu/arm-smmu: Clarify MMU-500 CPRE workaround

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Message-ID: <20241023143116.2981369-9-sashal@kernel.org>
Date: Wed, 23 Oct 2024 10:30:53 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Robin Murphy <robin.murphy@....com>,
	Will Deacon <will@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	joro@...tes.org,
	linux-arm-kernel@...ts.infradead.org,
	iommu@...ts.linux.dev
Subject: [PATCH AUTOSEL 6.6 09/23] iommu/arm-smmu: Clarify MMU-500 CPRE workaround

From: Robin Murphy <robin.murphy@....com>

[ Upstream commit 0dfe314cdd0d378f96bb9c6bdc05c8120f48606d ]

CPRE workarounds are implicated in at least 5 MMU-500 errata, some of
which remain unfixed. The comment and warning message have proven to be
unhelpfully misleading about this scope, so reword them to get the point
across with less risk of going out of date or confusing users.

Signed-off-by: Robin Murphy <robin.murphy@....com>
Link: https://lore.kernel.org/r/dfa82171b5248ad7cf1f25592101a6eec36b8c9a.1728400877.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/iommu/arm/arm-smmu/arm-smmu-impl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
index 9dc772f2cbb27..99030e6b16e7a 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
@@ -130,7 +130,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
 
 	/*
 	 * Disable MMU-500's not-particularly-beneficial next-page
-	 * prefetcher for the sake of errata #841119 and #826419.
+	 * prefetcher for the sake of at least 5 known errata.
 	 */
 	for (i = 0; i < smmu->num_context_banks; ++i) {
 		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
@@ -138,7 +138,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
 		arm_smmu_cb_write(smmu, i, ARM_SMMU_CB_ACTLR, reg);
 		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
 		if (reg & ARM_MMU500_ACTLR_CPRE)
-			dev_warn_once(smmu->dev, "Failed to disable prefetcher [errata #841119 and #826419], check ACR.CACHE_LOCK\n");
+			dev_warn_once(smmu->dev, "Failed to disable prefetcher for errata workarounds, check SACR.CACHE_LOCK\n");
 	}
 
 	return 0;
-- 
2.43.0