[PATCH RFC v2 1/8] spi: dt-bindings: spi-peripheral-props: add spi-offloads property

[David Lechner <dlechner@xxxxxxxxxxxx>]

This adds a new property to the spi-peripheral-props binding for use
with peripherals connected to controllers that support offloading.

Here, offloading means that the controller has the ability to perform
complex SPI transactions without CPU intervention in some shape or form.

This property will be used to assign controller offload resources to
each peripheral that needs them. What these resources are will be
defined by each specific controller binding.

Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
---

v2 changes:

In v1, instead of generic SPI bindings, there were only controller-
specific bindings, so this is a new patch.

In the previous version I also had an offloads object node that described
what the offload capabilities were but it was suggested that this was
not necessary/overcomplicated. So I've gone to the other extreme and
made it perhaps over-simplified now by requiring all information about
how each offload is used to be encoded in a single u32.

We could of course consider using #spi-offload-cells instead for
allowing encoding multiple parameters for each offload instance if that
would be preferable.

I also considered adding spi-offload-names that could be used as sort
of a compatible string (more of an interface name really) in case some
peripherals may want to support more than 1 specialized type of offload.
---
 .../devicetree/bindings/spi/spi-peripheral-props.yaml          | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
index 15938f81fdce..32991a2d2264 100644
--- a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
+++ b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
@@ -113,6 +113,16 @@ properties:
     minItems: 2
     maxItems: 4
 
+  spi-offloads:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    description:
+      Array of controller offload instances that are reserved for use by the
+      peripheral device. The semantic meaning of the values of the array
+      elements is defined by the controller. For example, it could be a simple
+      0-based index of the offload instance, or it could be a bitfield where
+      a few bits represent the assigned hardware trigger, a few bits represent
+      the assigned RX stream, etc.
+
   st,spi-midi-ns:
     description: |
       Only for STM32H7, (Master Inter-Data Idleness) minimum time

-- 
2.43.2