linux-kernel - [PATCH] iommu: Update "iommu.strict" documentation

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Message-Id: <2c8c06e1b449d6b060c5bf9ad3b403cd142f405d.1623682646.git.robin.murphy@arm.com>
Date:   Mon, 14 Jun 2021 15:57:26 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     joro@...tes.org
Cc:     will@...nel.org, john.garry@...wei.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        baolu.lu@...ux.intel.com
Subject: [PATCH] iommu: Update "iommu.strict" documentation

Consolidating the flush queue logic also meant that the "iommu.strict"
option started taking effect on x86 as well. Make sure we document that.

Fixes: a250c23f15c2 ("iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE")
Signed-off-by: Robin Murphy <robin.murphy@....com>
---
 Documentation/admin-guide/kernel-parameters.txt | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..20a32de990ed 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1987,7 +1987,7 @@
 			  forcing Dual Address Cycle for PCI cards supporting
 			  greater than 32-bit addressing.
 
-	iommu.strict=	[ARM64] Configure TLB invalidation behaviour
+	iommu.strict=	[ARM64, X86] Configure TLB invalidation behaviour
 			Format: { "0" | "1" }
 			0 - Lazy mode.
 			  Request that DMA unmap operations use deferred
@@ -1998,6 +1998,10 @@
 			1 - Strict mode (default).
 			  DMA unmap operations invalidate IOMMU hardware TLBs
 			  synchronously.
+			Note: on x86, the default behaviour depends on the
+			equivalent driver-specific parameters, but a strict
+			mode explicitly specified by either method takes
+			precedence.
 
 	iommu.passthrough=
 			[ARM64, X86] Configure DMA to bypass the IOMMU by default.
-- 
2.25.1