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

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Message-Id: <20250928075257.1542-1-guojinhui.liam@bytedance.com>
Date: Sun, 28 Sep 2025 15:52:57 +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] 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>
---
 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 ba9e582a8bbe..6e9eab365123 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3212,8 +3212,10 @@ static bool __init detect_ivrs(void)
 	}
 
 out:
-	/* Make sure ACS will be enabled during PCI probe */
-	pci_request_acs();
+	if (!amd_iommu_disabled || amd_iommu_force_enable) {
+		/* Make sure ACS will be enabled during PCI probe */
+		pci_request_acs();
+	}
 
 	return true;
 }
-- 
2.20.1