Describe the SIO coprocessor which serves as pretend DMA controller on recent Apple platforms. Signed-off-by: Martin Povišer <povik+lin@xxxxxxxxxxx> --- 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 <povik+lin@xxxxxxxxxxx> + +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
