[PATCH v4 1/3] dt-bindings: ata: eswin: Document for EIC7700 SoC ahci

[Yulin Lu <luyulin@eswincomputing.com>]

Document the SATA AHCI controller on the EIC7700 SoC platform,
including descriptions of its hardware configurations.

Retains the "ports-implemented" property in the DTS, because
removing it and relying only on the firmware register causes
problems. If the property is not present and we remove the
module using `rmmod`, a reset is triggered that clears the
register. As a result, inserting module again using `insmod`
will lead to errors.

The detailed reasons are that the ports-implemented register is
configured by the firmware (U-Boot on the HiFive Premier P550 board)
before kernel entry and correctly set to 0x1. During probe,
ahci_platform_enable_resources() -> ahci_platform_deassert_rsts() is
called, and when the driver is removed,
ahci_platform_disable_resources() -> ahci_platform_assert_rsts() is
called. This reset clears the register, which is defined by the IP
databook to reset to 0.

Signed-off-by: Yulin Lu <luyulin@eswincomputing.com>
---
 .../bindings/ata/eswin,eic7700-ahci.yaml      | 79 +++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/ata/eswin,eic7700-ahci.yaml

diff --git a/Documentation/devicetree/bindings/ata/eswin,eic7700-ahci.yaml b/Documentation/devicetree/bindings/ata/eswin,eic7700-ahci.yaml
new file mode 100644
index 000000000000..40c44f0705ba
--- /dev/null
+++ b/Documentation/devicetree/bindings/ata/eswin,eic7700-ahci.yaml
@@ -0,0 +1,79 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/ata/eswin,eic7700-ahci.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Eswin EIC7700 SoC SATA Controller
+
+maintainers:
+  - Yulin Lu <luyulin@eswincomputing.com>
+  - Huan He <hehuan1@eswincomputing.com>
+
+description:
+  AHCI SATA controller embedded into the EIC7700 SoC
+  is based on the DWC AHCI SATA v5.00a IP core.
+
+select:
+  properties:
+    compatible:
+      const: eswin,eic7700-ahci
+  required:
+    - compatible
+
+allOf:
+  - $ref: snps,dwc-ahci-common.yaml#
+
+properties:
+  compatible:
+    items:
+      - const: eswin,eic7700-ahci
+      - const: snps,dwc-ahci
+
+  clocks:
+    minItems: 2
+    maxItems: 2
+
+  clock-names:
+    items:
+      - const: pclk
+      - const: aclk
+
+  resets:
+    maxItems: 1
+
+  reset-names:
+    const: arst
+
+  ports-implemented:
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+  - resets
+  - reset-names
+  - phys
+  - phy-names
+  - ports-implemented
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    sata@50420000 {
+        compatible = "eswin,eic7700-ahci", "snps,dwc-ahci";
+        reg = <0x50420000 0x10000>;
+        interrupt-parent = <&plic>;
+        interrupts = <58>;
+        clocks = <&clock 171>, <&clock 186>;
+        clock-names = "pclk", "aclk";
+        phys = <&sata_phy>;
+        phy-names = "sata-phy";
+        ports-implemented = <0x1>;
+        resets = <&reset 96>;
+        reset-names = "arst";
+    };
-- 
2.25.1