docs: driver-api: add xilinx driver API documentation

The current file there (emmi) provides a description of
the driver uAPI and kAPI.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/driver-api/xilinx/eemi.rst

@@ -0,0 +1,67 @@
+====================================
+Xilinx Zynq MPSoC EEMI Documentation
+====================================
+
+Xilinx Zynq MPSoC Firmware Interface
+-------------------------------------
+The zynqmp-firmware node describes the interface to platform firmware.
+ZynqMP has an interface to communicate with secure firmware. Firmware
+driver provides an interface to firmware APIs. Interface APIs can be
+used by any driver to communicate with PMC(Platform Management Controller).
+
+Embedded Energy Management Interface (EEMI)
+----------------------------------------------
+The embedded energy management interface is used to allow software
+components running across different processing clusters on a chip or
+device to communicate with a power management controller (PMC) on a
+device to issue or respond to power management requests.
+
+EEMI ops is a structure containing all eemi APIs supported by Zynq MPSoC.
+The zynqmp-firmware driver maintain all EEMI APIs in zynqmp_eemi_ops
+structure. Any driver who want to communicate with PMC using EEMI APIs
+can call zynqmp_pm_get_eemi_ops().
+
+Example of EEMI ops::
+
+	/* zynqmp-firmware driver maintain all EEMI APIs */
+	struct zynqmp_eemi_ops {
+		int (*get_api_version)(u32 *version);
+		int (*query_data)(struct zynqmp_pm_query_data qdata, u32 *out);
+	};
+
+	static const struct zynqmp_eemi_ops eemi_ops = {
+		.get_api_version = zynqmp_pm_get_api_version,
+		.query_data = zynqmp_pm_query_data,
+	};
+
+Example of EEMI ops usage::
+
+	static const struct zynqmp_eemi_ops *eemi_ops;
+	u32 ret_payload[PAYLOAD_ARG_CNT];
+	int ret;
+
+	eemi_ops = zynqmp_pm_get_eemi_ops();
+	if (IS_ERR(eemi_ops))
+		return PTR_ERR(eemi_ops);
+
+	ret = eemi_ops->query_data(qdata, ret_payload);
+
+IOCTL
+------
+IOCTL API is for device control and configuration. It is not a system
+IOCTL but it is an EEMI API. This API can be used by master to control
+any device specific configuration. IOCTL definitions can be platform
+specific. This API also manage shared device configuration.
+
+The following IOCTL IDs are valid for device control:
+- IOCTL_SET_PLL_FRAC_MODE	8
+- IOCTL_GET_PLL_FRAC_MODE	9
+- IOCTL_SET_PLL_FRAC_DATA	10
+- IOCTL_GET_PLL_FRAC_DATA	11
+
+Refer EEMI API guide [0] for IOCTL specific parameters and other EEMI APIs.
+
+References
+----------
+[0] Embedded Energy Management Interface (EEMI) API guide:
+    https://www.xilinx.com/support/documentation/user_guides/ug1200-eemi-api.pdf

Documentation/driver-api/xilinx/index.rst

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+
+===========
+Xilinx FPGA
+===========
+
+.. toctree::
+    :maxdepth: 1
+
+    eemi
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`