linux-kernel - [PATCH v2 1/4] dt-bindings: reserved-memory: Document "active" property

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Message-Id: <20200904130000.691933-1-thierry.reding@gmail.com>
Date:   Fri,  4 Sep 2020 14:59:57 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/4] dt-bindings: reserved-memory: Document "active" property

From: Thierry Reding <treding@...dia.com>

Reserved memory regions can be marked as "active" if hardware is
expected to access the regions during boot and before the operating
system can take control. One example where this is useful is for the
operating system to infer whether the region needs to be identity-
mapped through an IOMMU.

Signed-off-by: Thierry Reding <treding@...dia.com>
---
 .../bindings/reserved-memory/reserved-memory.txt           | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
index 4dd20de6977f..163d2927e4fc 100644
--- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+++ b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
@@ -63,6 +63,13 @@ reusable (optional) - empty property
       able to reclaim it back. Typically that means that the operating
       system can use that region to store volatile or cached data that
       can be otherwise regenerated or migrated elsewhere.
+active (optional) - empty property
+    - If this property is set for a reserved memory region, it indicates
+      that some piece of hardware may be actively accessing this region.
+      Should the operating system want to enable IOMMU protection for a
+      device, all active memory regions must have been identity-mapped
+      in order to ensure that non-quiescent hardware during boot can
+      continue to access the memory.
 
 Linux implementation note:
 - If a "linux,cma-default" property is present, then Linux will use the
-- 
2.28.0