The current DT bindings assume that the DMA will be performed by the
devices through their parent DT node, and rely on that assumption for the
address translation using dma-ranges.
However, some SoCs have devices that will perform DMA through another bus,
with separate address translation rules. We therefore need to express that
relationship, through the dma-parent property.
Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
---
Documentation/devicetree/booting-without-of.txt | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
index e86bd2f64117..4a65c943c02d 100644
--- a/Documentation/devicetree/booting-without-of.txt
+++ b/Documentation/devicetree/booting-without-of.txt
@@ -1403,8 +1403,15 @@ In addition, each DMA master device on the DMA bus may or may not support
coherent DMA operations. The "dma-coherent" property is intended to be used
for identifying devices supported coherent DMA operations in DT.
+Some devices will also perform DMA through another bus than their parent
+control bus. In such a case, the "dma-parent" property is intended to express
+that relationship to another device in DT that will be the DMA parent bus.
+
* DMA Bus master
Optional property:
+- #dma-parent-cells: <integer>
+ The #dma-parent-cells property defines the width of the cells used to
+ represent the DMA parent.
- dma-ranges: <prop-encoded-array> encoded as arbitrary number of triplets of
(child-bus-address, parent-bus-address, length). Each triplet specified
describes a contiguous DMA address range.
@@ -1420,6 +1427,9 @@ Optional property:
- dma-ranges: <empty> value. if present - It means that DMA addresses
translation has to be enabled for this device.
- dma-coherent: Present if dma operations are coherent
+- dma-parent: List of phandles and their optional arguments according to the
+ #dma-parent-cells from the provider. Expresses the routing of DMA if it
+ doesn't go through the parent node, but some other node in the device tree.
Example:
soc {
--
git-series 0.9.1
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