[PATCH v8 16/18] dt-bindings: clock: imx8m-clock: support spread spectrum clocking

[Dario Binacchi <dario.binacchi@amarulasolutions.com>]

The addition of DT bindings for enabling and tuning spread spectrum
clocking generation can be applied specifically to the PLLs.

The "" value for the fsl,ssc-method property is specifically intended to
specify a "no SSC" case, as in the example, when you don't want to
configure spread spectrum for one of the PLLs, thus avoiding the use of
a method that would only make sense if SSC were being set.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

---

(no changes since v7)

Changes in v7:
- List the PLLs to strictly define the setup order for each of the
  added properties
- Drop maxItems from "fsl,ssc-modfreq-hz" and "fsl,ssc-modrate-percent"
  properties
- Add 'Reviewed-by' tag of Krzysztof Kozlowski

Changes in v6:
- Improve the commit message
- change minItems from 7 to 1 for all the ssc properties added
- change maxItems from 10 to 4 for alle the ssc properties added
- update the DTS example

Changes in v4:
- Drop "fsl,ssc-clocks" property. The other added properties now refer
  to the clock list.
- Updated minItems and maxItems of
  - clocks
  - clock-names
  - fsl,ssc-modfreq-hz
  - fsl,ssc-modrate-percent
  - fsl,ssc-modmethod
- Updated the dts examples

Changes in v3:
- Added in v3
- The dt-bindings have been moved from fsl,imx8m-anatop.yaml to
  imx8m-clock.yaml. The anatop device (fsl,imx8m-anatop.yaml) is
  indeed more or less a syscon, so it represents a memory area
  accessible by ccm (imx8m-clock.yaml) to setup the PLLs.

Changes in v2:
- Add "allOf:" and place it after "required:" block, like in the
  example schema.
- Move the properties definition to the top-level.
- Drop unit types as requested by the "make dt_binding_check" command.

 .../bindings/clock/imx8m-clock.yaml           | 47 +++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
index d96570bf60dc..d347d630764a 100644
--- a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
+++ b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
@@ -43,6 +43,46 @@ properties:
       ID in its "clocks" phandle cell. See include/dt-bindings/clock/imx8m-clock.h
       for the full list of i.MX8M clock IDs.
 
+  fsl,ssc-modfreq-hz:
+    description:
+      The values of modulation frequency (Hz unit) for each clock
+      supporting spread spectrum.
+    minItems: 1
+    items:
+      - description: audio_pll1
+      - description: audio_pll2
+      - description: dram_pll
+      - description: video_pll
+
+  fsl,ssc-modrate-percent:
+    description:
+      The percentage values of modulation rate for each clock
+      supporting spread spectrum.
+    minItems: 1
+    items:
+      - description: audio_pll1
+      - description: audio_pll2
+      - description: dram_pll
+      - description: video_pll
+
+  fsl,ssc-modmethod:
+    $ref: /schemas/types.yaml#/definitions/non-unique-string-array
+    description: |
+      The modulation techniques for each clock supporting spread
+      spectrum in this order::
+      - audio_pll1
+      - audio_pll2
+      - dram_pll
+      - video_pll
+    minItems: 1
+    maxItems: 4
+    items:
+      enum:
+        - ""
+        - down-spread
+        - up-spread
+        - center-spread
+
 required:
   - compatible
   - reg
@@ -76,6 +116,10 @@ allOf:
             - const: clk_ext2
             - const: clk_ext3
             - const: clk_ext4
+        fsl,ssc-modfreq-hz: false
+        fsl,ssc-modrate-percent: false
+        fsl,ssc-modmethod: false
+
     else:
       properties:
         clocks:
@@ -124,6 +168,9 @@ examples:
         clock-names = "osc_32k", "osc_24m", "clk_ext1", "clk_ext2",
                       "clk_ext3", "clk_ext4", "audio_pll1", "audio_pll2",
                       "dram_pll", "video_pll";
+        fsl,ssc-modfreq-hz = <6818>, <0>, <0>, <2419>;
+        fsl,ssc-modrate-percent = <3>, <0>, <0>, <7>;
+        fsl,ssc-modmethod = "down-spread", "", "", "center-spread";
     };
 
   - |
-- 
2.43.0