scsi: ufs: dt-bindings: Document static TX Equalization settings properties

UFS v5.0/UFSHCI v5.0 adds HS-G6 support (46.6 Gbps/lane) via UniPro v3.0
and M-PHY v6.0. These specs define TX Equalization for all High-Speed Gears
(not only HS-G6) to compensate channel loss and improve signal integrity at
high speed.

For HS-G6, M-PHY uses PAM4 1b1b line coding. Pre-Coding may also be
required depending on channel characteristics.

Document vendor-neutral properties in ufs-common.yaml:

 - txeq-preshoot-g[1-6]

 - txeq-deemphasis-g[1-6]

 - tx-precode-enable-g6

Values are per-lane Host/Device tuples (2 values for x1, 4 values for
x2). PreShoot/DeEmphasis range from 0..7, and Precode is 0/1.

These are board-specific signal-integrity tuning values. They depend on
channel SI/PHY characterization and validation (host PHY, device PHY,
package, and board routing), and are determined by HW/PHY designers.

Although UFSHCI v5.0 supports TX Equalization Training via UniPro v3.0,
which allows host software to determine optimal TX Equalization at
runtime, static board-specific TX Equalization settings in the Device

Tree are still necessary because:

 - TX Equalization Training is not supported for HS-G3 and below

 - TX Equalization Training is disabled on some platforms

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Peter Wang <peter.wang@mediatek.com>
Signed-off-by: Can Guo <can.guo@oss.qualcomm.com>
Link: https://patch.msgid.link/20260616113348.1168248-2-can.guo@oss.qualcomm.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/devicetree/bindings/ufs/ufs-common.yaml

@@ -105,6 +105,64 @@ properties:
       Restricts the UFS controller to rate-a or rate-b for both TX and
       RX directions.
 
+  tx-precode-enable-g6:
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    minItems: 1
+    items:
+      - items:
+          - description: Host_Lane0 precode
+            enum: [0, 1]
+          - description: Device_Lane0 precode
+            enum: [0, 1]
+      - items:
+          - description: Host_Lane1 precode
+            enum: [0, 1]
+          - description: Device_Lane1 precode
+            enum: [0, 1]
+    description:
+      Static TX Precode enable values for HS-G6 only.
+
+patternProperties:
+  "^txeq-preshoot-g[1-6]$":
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    minItems: 1
+    items:
+      - items:
+          - description: Host_Lane0 Preshoot value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+          - description: Device_Lane0 Preshoot value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+      - items:
+          - description: Host_Lane1 Preshoot value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+          - description: Device_Lane1 Preshoot value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+    description: |
+      Static TX Equalization PreShoot settings for High Speed Gears. These
+      values are programmed to the corresponding UniPro PA layer attribute
+      PA_TxEQG[1-6]Setting. Each value selects a Pre-Shoot level as defined
+      by the MIPI M-PHY specification (TX_HS_PreShoot_Setting).
+
+  "^txeq-deemphasis-g[1-6]$":
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    minItems: 1
+    items:
+      - items:
+          - description: Host_Lane0 DeEmphasis value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+          - description: Device_Lane0 DeEmphasis value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+      - items:
+          - description: Host_Lane1 DeEmphasis value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+          - description: Device_Lane1 DeEmphasis value
+            enum: [0, 1, 2, 3, 4, 5, 6, 7]
+    description: |
+      Static TX Equalization DeEmphasis settings for High Speed Gears. These
+      values are programmed to the corresponding UniPro PA layer attribute
+      PA_TxEQG[1-6]Setting. Each value selects a De-Emphasis level as defined
+      by the MIPI M-PHY specification (TX_HS_DeEmphasis_Setting).
+
 dependencies:
   freq-table-hz: [ clocks ]
   operating-points-v2: [ clocks, clock-names ]