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@bootlin.com --- 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 {