linux-kernel - [PATCH v2 1/1] iommu/amd: Enable PCIe ACS only if AMD IOMMU is on

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Message-Id: <20251011031448.2699-2-guojinhui.liam@bytedance.com>
Date: Sat, 11 Oct 2025 11:14:48 +0800
From: Jinhui Guo <guojinhui.liam@...edance.com>
To: joro@...tes.org,
	suravee.suthikulpanit@....com
Cc: guojinhui.liam@...edance.com,
	iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/1] iommu/amd: Enable PCIe ACS only if AMD IOMMU is on

To preserve PCIe performance, ACS is enabled only when
AMD IOMMU is not disabled.

Signed-off-by: Jinhui Guo <guojinhui.liam@...edance.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 drivers/iommu/amd/init.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index f2991c11867c..38e8c38c5f10 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3314,8 +3314,10 @@ static bool __init detect_ivrs(void)
 	}
 
 out:
-	/* Make sure ACS will be enabled during PCI probe */
-	pci_request_acs();
+	if (!amd_iommu_disabled) {
+		/* Make sure ACS will be enabled during PCI probe */
+		pci_request_acs();
+	}
 
 	return true;
 }
-- 
2.20.1