[RFC PATCH 3/3] spi: dt-bindings: zynqmp: Describe dual stacked/parallel memories modes

[Miquel Raynal]

Describe the two dual memories modes which are available on the ZynqMP
QSPI controller: stacked and parallel.

Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
---
 .../bindings/spi/spi-zynqmp-qspi.yaml         | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml b/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml
index ea72c8001256..959e008602f5 100644
--- a/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml
+++ b/Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.yaml
@@ -30,6 +30,28 @@ properties:
   clocks:
     maxItems: 2
 
+  xlnx,dual-stacked-memories:
+    type: boolean
+    description: The QSPI controller can be wired to two SPI memorie in stacked
+      mode. This basically means that the two devices share the same bus but
+      have their own chip-select. From the controller perspective, it is like
+      having a single big device, the most significant addressing bit
+      automatically driving one chip-select or the other. This basically doubles
+      the total address space with only a single additional wire. Note that when
+      configured in dual-stacked mode, the controller does not support XIP nor
+      linear addressing.
+
+  xlnx,dual-parallel-memories:
+    type: boolean
+    description: The QSPI controller can be wired to two SPI memorie in parallel
+      mode. The two devices physically are on different buses but will always
+      act synchronously as for each byte, the even bits are stored in one memory
+      and the odd bits are stored in the other. From the controller perspective,
+      it is like having a single big device with a much higher throughput. This
+      basically uses two quad devices as if it was a single octal device. Note
+      that when configured in dual-parallel mode, the controller does not
+      support XIP nor linear addressing.
+
 unevaluatedProperties: false
 
 examples:
@@ -47,5 +69,14 @@ examples:
         interrupt-parent = <&gic>;
         reg = <0x0 0xff0f0000 0x0 0x1000>,
               <0x0 0xc0000000 0x0 0x8000000>;
+        #address-cells = <2>;
+        #size-cells = <0>;
+        xlnx,dual-stacked-memories;
+
+        flash at 0,1 {
+          compatible = "jedec,spi-nor";
+          spi-max-frequency = <50000000>;
+          reg = <0>, <1>;
+        };
       };
     };
-- 
2.27.0