dt-bindings: bus: add device tree bindings for qcom,ssc-block-bus

Adds bindings for the AHB bus which exposes the SSC block in the global
address space. This bus (and the SSC block itself) is present on certain
qcom SoCs.

In typical configuration, this bus (as some of the clocks and registers
that we need to manipulate) is not accessible to the OS, and the
resources on this bus are indirectly accessed by communicating with a
hexagon CPU core residing in the SSC block. In this configuration, the
hypervisor is the one performing the bus initialization for the purposes
of bringing the haxagon CPU core out of reset.

However, it is possible to change the configuration, in which case this
binding serves to allow the OS to initialize the bus.
Signed-off-by: Michael Srba <Michael.Srba@seznam.cz>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220411072156.24451-4-michael.srba@seznam.cz

Documentation/devicetree/bindings/bus/qcom,ssc-block-bus.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/bus/qcom,ssc-block-bus.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: The AHB Bus Providing a Global View of the SSC Block on (some) qcom SoCs
+
+maintainers:
+  - Michael Srba <Michael.Srba@seznam.cz>
+
+description: |
+  This binding describes the dependencies (clocks, resets, power domains) which
+  need to be turned on in a sequence before communication over the AHB bus
+  becomes possible.
+
+  Additionally, the reg property is used to pass to the driver the location of
+  two sadly undocumented registers which need to be poked as part of the sequence.
+
+  The SSC (Snapdragon Sensor Core) block contains a gpio controller, i2c/spi/uart
+  controllers, a hexagon core, and a clock controller which provides clocks for
+  the above.
+
+properties:
+  compatible:
+    items:
+      - const: qcom,msm8998-ssc-block-bus
+      - const: qcom,ssc-block-bus
+
+  reg:
+    description: |
+      Shall contain the addresses of the SSCAON_CONFIG0 and SSCAON_CONFIG1
+      registers
+    minItems: 2
+    maxItems: 2
+
+  reg-names:
+    items:
+      - const: mpm_sscaon_config0
+      - const: mpm_sscaon_config1
+
+  '#address-cells':
+    enum: [ 1, 2 ]
+
+  '#size-cells':
+    enum: [ 1, 2 ]
+
+  ranges: true
+
+  clocks:
+    minItems: 6
+    maxItems: 6
+
+  clock-names:
+    items:
+      - const: xo
+      - const: aggre2
+      - const: gcc_im_sleep
+      - const: aggre2_north
+      - const: ssc_xo
+      - const: ssc_ahbs
+
+  power-domains:
+    description: Power domain phandles for the ssc_cx and ssc_mx power domains
+    minItems: 2
+    maxItems: 2
+
+  power-domain-names:
+    items:
+      - const: ssc_cx
+      - const: ssc_mx
+
+  resets:
+    description: |
+      Reset phandles for the ssc_reset and ssc_bcr resets (note: ssc_bcr is the
+      branch control register associated with the ssc_xo and ssc_ahbs clocks)
+    minItems: 2
+    maxItems: 2
+
+  reset-names:
+    items:
+      - const: ssc_reset
+      - const: ssc_bcr
+
+  qcom,halt-regs:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    description: describes how to locate the ssc AXI halt register
+    items:
+      - items:
+          - description: Phandle reference to a syscon representing TCSR
+          - description: offset for the ssc AXI halt register
+
+required:
+  - compatible
+  - reg
+  - reg-names
+  - '#address-cells'
+  - '#size-cells'
+  - ranges
+  - clocks
+  - clock-names
+  - power-domains
+  - power-domain-names
+  - resets
+  - reset-names
+  - qcom,halt-regs
+
+additionalProperties:
+  type: object
+
+examples:
+  - |
+    #include <dt-bindings/clock/qcom,gcc-msm8998.h>
+    #include <dt-bindings/clock/qcom,rpmcc.h>
+    #include <dt-bindings/power/qcom-rpmpd.h>
+
+    soc {
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        // devices under this node are physically located in the SSC block, connected to an ssc-internal bus;
+        ssc_ahb_slave: bus@10ac008 {
+            #address-cells = <1>;
+            #size-cells = <1>;
+            ranges;
+
+            compatible = "qcom,msm8998-ssc-block-bus", "qcom,ssc-block-bus";
+            reg = <0x10ac008 0x4>, <0x10ac010 0x4>;
+            reg-names = "mpm_sscaon_config0", "mpm_sscaon_config1";
+
+            clocks = <&xo>,
+                     <&rpmcc RPM_SMD_AGGR2_NOC_CLK>,
+                     <&gcc GCC_IM_SLEEP>,
+                     <&gcc AGGRE2_SNOC_NORTH_AXI>,
+                     <&gcc SSC_XO>,
+                     <&gcc SSC_CNOC_AHBS_CLK>;
+            clock-names = "xo", "aggre2", "gcc_im_sleep", "aggre2_north", "ssc_xo", "ssc_ahbs";
+
+            resets = <&gcc GCC_SSC_RESET>, <&gcc GCC_SSC_BCR>;
+            reset-names = "ssc_reset", "ssc_bcr";
+
+            power-domains = <&rpmpd MSM8998_SSCCX>, <&rpmpd MSM8998_SSCMX>;
+            power-domain-names = "ssc_cx", "ssc_mx";
+
+            qcom,halt-regs = <&tcsr_mutex_regs 0x26000>;
+        };
+    };