Describe the SIO coprocessor which serves as pretend DMA controller on
recent Apple platforms.
Signed-off-by: Martin Povišer <[email protected]>
---
Since v1:
- formatting fixes requested by Rob
- dropped provider nodes from example
- added 'memory-region' items range
- tweaked 'apple,sio-firmware-params' description
Since the schema mentions a loader preparing the binding appropriately,
here's a PR with the relevant (WIP) loader code, if anyone wants to look:
https://github.com/AsahiLinux/m1n1/pull/286
.../devicetree/bindings/dma/apple,sio.yaml | 111 ++++++++++++++++++
1 file changed, 111 insertions(+)
create mode 100644 Documentation/devicetree/bindings/dma/apple,sio.yaml
diff --git a/Documentation/devicetree/bindings/dma/apple,sio.yaml b/Documentation/devicetree/bindings/dma/apple,sio.yaml
new file mode 100644
index 000000000000..0e3780ad9dd7
--- /dev/null
+++ b/Documentation/devicetree/bindings/dma/apple,sio.yaml
@@ -0,0 +1,111 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/dma/apple,sio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Apple SIO Coprocessor
+
+description:
+ SIO is a coprocessor on Apple M1 and later chips (and maybe also on earlier
+ chips). Its role is to offload SPI, UART and DisplayPort audio transfers,
+ being a pretend DMA controller.
+
+maintainers:
+ - Martin Povišer <[email protected]>
+
+allOf:
+ - $ref: dma-controller.yaml#
+
+properties:
+ compatible:
+ items:
+ - enum:
+ - apple,t6000-sio
+ - apple,t8103-sio
+ - const: apple,sio
+
+ reg:
+ maxItems: 1
+
+ '#dma-cells':
+ const: 1
+ description:
+ DMA clients specify a single cell that corresponds to the RTKit endpoint
+ number used for arranging the transfers in question
+
+ dma-channels:
+ maximum: 128
+
+ mboxes:
+ maxItems: 1
+
+ iommus:
+ maxItems: 1
+
+ power-domains:
+ maxItems: 1
+
+ memory-region:
+ minItems: 2
+ maxItems: 8
+ description:
+ A number of references to reserved memory regions among which are the DATA/TEXT
+ sections of coprocessor executable firmware and also auxiliary firmware data
+ describing the available DMA-enabled peripherals
+
+ apple,sio-firmware-params:
+ $ref: /schemas/types.yaml#/definitions/uint32-array
+ description: |
+ Parameters in the form of opaque key/value pairs that are to be sent to the SIO
+ coprocesssor once it boots. These parameters can point into the reserved memory
+ regions (in device address space).
+
+ Note that unlike Apple's firmware, we treat the parameters, and the data they
+ refer to, as opaque. Apple embed short data blobs into their SIO devicetree node
+ that describe the DMA-enabled peripherals (presumably with defined semantics).
+ Their driver processes those blobs and sets up data structure in mapped device
+ memory, then references this memory in the parameters sent to the SIO. At the
+ level of description we are opting for in this binding, we assume the job of
+ constructing those data structures has been done in advance, leaving behind an
+ opaque list of key/value parameter pairs to be sent by a prospective driver.
+
+ This approach is chosen for two reasons:
+
+ - It means we don't need to try to understand the semantics of Apple's blobs
+ as long as we know the transformation we need to do from Apple's devicetree
+ data to SIO data (which can be shoved away into a loader). It also means the
+ semantics of Apple's blobs (or of something to replace them) need not be part
+ of the binding and be kept up with Apple's firmware changes in the future.
+
+ - It leaves less work for the driver attaching on this binding. Instead the work
+ is done upfront in the loader which can be better suited for keeping up with
+ Apple's firmware changes.
+
+required:
+ - compatible
+ - reg
+ - '#dma-cells'
+ - dma-channels
+ - mboxes
+ - iommus
+ - power-domains
+
+additionalProperties: false
+
+examples:
+ - |
+ sio: dma-controller@36400000 {
+ compatible = "apple,t8103-sio", "apple,sio";
+ reg = <0x36400000 0x8000>;
+ dma-channels = <128>;
+ #dma-cells = <1>;
+ mboxes = <&sio_mbox>;
+ iommus = <&sio_dart 0>;
+ power-domains = <&ps_sio_cpu>;
+ memory-region = <&sio_text>, <&sio_data>,
+ <&sio_auxdata1>, <&sio_auxdata2>; /* Filled by loader */
+ apple,sio-firmware-params = <0xb 0x10>, <0xc 0x1b80>, <0xf 0x14>,
+ <0x10 0x1e000>, <0x30d 0x34>, <0x30e 0x4000>,
+ <0x1a 0x38>, <0x1b 0x50>; /* Filled by loader */
+ };
--
2.33.0
On Tue, 14 Feb 2023 21:36:37 +0100, Martin Povišer wrote:
> Describe the SIO coprocessor which serves as pretend DMA controller on
> recent Apple platforms.
>
> Signed-off-by: Martin Povišer <[email protected]>
> ---
> Since v1:
> - formatting fixes requested by Rob
> - dropped provider nodes from example
> - added 'memory-region' items range
> - tweaked 'apple,sio-firmware-params' description
>
> Since the schema mentions a loader preparing the binding appropriately,
> here's a PR with the relevant (WIP) loader code, if anyone wants to look:
> https://github.com/AsahiLinux/m1n1/pull/286
>
>
> .../devicetree/bindings/dma/apple,sio.yaml | 111 ++++++++++++++++++
> 1 file changed, 111 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/dma/apple,sio.yaml
>
Reviewed-by: Rob Herring <[email protected]>