schemas: pci: bridge: Document PCIe equalization presets

PCIe equalization presets are predefined settings used to optimize
signal integrity by compensating for signal loss and distortion in
high-speed data transmission.

As per PCIe spec 6.0.1 revision section 8.3.3.3 & 4.2.4 for data rates
of  8.0 GT/s, 16.0 GT/s, 32.0 GT/s and 64.0 GT/s provides a way to
configure lane equalization presets for each lane to enhance the PCIe
link reliability. Each preset value represents a different combination
of pre-shoot and de-emphasis values.

For each data rate it may be required to have a different preset
configuration and each lane will have different preset values.

Define per data rate equalization preset property with array of 16
representing 16 lanes of the PCIe.

Signed-off-by: Krishna chaitanya chundru <[email protected]>

dtschema/schemas/pci/pci-bus-common.yaml

@@ -159,6 +159,42 @@ properties:
   vpcie3v3aux-supply:
     description: 3.3v AUX regulator phandle for the slot
 
+  eq-presets-8gts:
+    description:
+      Contains the equalization preset values for PCIe data rates 8.0 GT/s.
+      Each preset value is used to adjust the transmitter settings to improve
+      signal quality and meet the electrical requirements.
+    $ref: /schemas/types.yaml#/definitions/uint16-array
+    minItems: 1
+    maxItems: 16
+
+  eq-presets-16gts:
+    description:
+      Contains the equalization preset values for PCIe data rates 16.0 GT/s.
+      Each preset value is used to adjust the transmitter settings to improve
+      signal quality and meet the electrical requirements.
+    $ref: /schemas/types.yaml#/definitions/uint8-array
+    minItems: 1
+    maxItems: 16
+
+  eq-presets-32gts:
+    description:
+      Contains the equalization preset values for PCIe data rates 32.0 GT/s.
+      Each preset value is used to adjust the transmitter settings to improve
+      signal quality and meet the electrical requirements.
+    $ref: /schemas/types.yaml#/definitions/uint8-array
+    minItems: 1
+    maxItems: 16
+
+  eq-presets-64gts:
+    description:
+      Contains the equalization preset values for PCIe data rates 64.0 GT/s.
+      Each preset value is used to adjust the transmitter settings to improve
+      signal quality and meet the electrical requirements.
+    $ref: /schemas/types.yaml#/definitions/uint8-array
+    minItems: 1
+    maxItems: 16
+
 patternProperties:
   "@1?[0-9a-f](,[0-7])?$":
     type: object