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From:   Bjorn Andersson <quic_bjorande@quicinc.com>
To:     Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>
CC:     <linux-arm-msm@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH v2 1/3] dt-bindings: reserved-memory: rmtfs: Allow guard pages
Date:   Tue, 30 May 2023 16:36:41 -0700
Message-ID: <20230530233643.4044823-2-quic_bjorande@quicinc.com>
In-Reply-To: <20230530233643.4044823-1-quic_bjorande@quicinc.com>
References: <20230530233643.4044823-1-quic_bjorande@quicinc.com>
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On some Qualcomm platforms it's required that the rmtfs memory is not
placed adjacent to allocations performed by other clients. Some
DeviceTree authors have solved this by reserving the space around
the region, but this prevents such author to use rely on the OS to place
the region, through the use of "size" (instead of a fixed location).

So introduce a flag to indicate that guard pages should be carved at the
beginning and end of the memory region. The user shall account for the
two 4k blocks in the defined size.

Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
---

Changes since v1:
- Drop qcom,alloc-size in favour of using reserved-memory/size
- Introduce explicit property to signal that guard pages should be
  carved out from this region (rather than always do it in the dynamic
  case).

 .../bindings/reserved-memory/qcom,rmtfs-mem.yaml           | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/reserved-memory/qcom,rmtfs-mem.yaml b/Documentation/devicetree/bindings/reserved-memory/qcom,rmtfs-mem.yaml
index bab982f00485..26e24e7b08cf 100644
--- a/Documentation/devicetree/bindings/reserved-memory/qcom,rmtfs-mem.yaml
+++ b/Documentation/devicetree/bindings/reserved-memory/qcom,rmtfs-mem.yaml
@@ -26,6 +26,13 @@ properties:
     description: >
       identifier of the client to use this region for buffers
 
+  qcom,use-guard-pages:
+    type: boolean
+    description: >
+      Indicates that the OS should ignore the first and last 4k block of the
+      memory region, for the purpose of ensuring that the allocation is not
+      adjacent to other protected regions.
+
   qcom,vmid:
     $ref: /schemas/types.yaml#/definitions/uint32-array
     description: >
-- 
2.25.1