Documentation/amdgpu: Add PM policy documentation

Add documentation about the newly added pm_policy node in sysfs.
Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Documentation/gpu/amdgpu/thermal.rst

@@ -49,6 +49,12 @@ pp_power_profile_mode
 .. kernel-doc:: drivers/gpu/drm/amd/pm/amdgpu_pm.c
    :doc: pp_power_profile_mode
 
+pm_policy
+---------------------
+
+.. kernel-doc:: drivers/gpu/drm/amd/pm/amdgpu_pm.c
+   :doc: pm_policy
+
 \*_busy_percent
 ---------------
 

drivers/gpu/drm/amd/pm/amdgpu_pm.c

@@ -2220,6 +2220,59 @@ struct amdgpu_pm_policy_attr {
 	enum pp_pm_policy id;
 };
 
+/**
+ * DOC: pm_policy
+ *
+ * Certain SOCs can support different power policies to optimize application
+ * performance. However, this policy is provided only at SOC level and not at a
+ * per-process level. This is useful especially when entire SOC is utilized for
+ * dedicated workload.
+ *
+ * The amdgpu driver provides a sysfs API for selecting the policy. Presently,
+ * only two types of policies are supported through this interface.
+ *
+ *  Pstate Policy Selection - This is to select different Pstate profiles which
+ *  decides clock/throttling preferences.
+ *
+ *  XGMI PLPD Policy Selection - When multiple devices are connected over XGMI,
+ *  this helps to select policy to be applied for per link power down.
+ *
+ * The list of available policies and policy levels vary between SOCs. They can
+ * be viewed under pm_policy node directory. If SOC doesn't support any policy,
+ * this node won't be available. The different policies supported will be
+ * available as separate nodes under pm_policy.
+ *
+ *	cat /sys/bus/pci/devices/.../pm_policy/<policy_type>
+ *
+ * Reading the policy file shows the different levels supported. The level which
+ * is applied presently is denoted by * (asterisk). E.g.,
+ *
+ * .. code-block:: console
+ *
+ *	cat /sys/bus/pci/devices/.../pm_policy/soc_pstate
+ *	0 : soc_pstate_default
+ *	1 : soc_pstate_0
+ *	2 : soc_pstate_1*
+ *	3 : soc_pstate_2
+ *
+ *	cat /sys/bus/pci/devices/.../pm_policy/xgmi_plpd
+ *	0 : plpd_disallow
+ *	1 : plpd_default
+ *	2 : plpd_optimized*
+ *
+ * To apply a specific policy
+ *
+ * "echo  <level> > /sys/bus/pci/devices/.../pm_policy/<policy_type>"
+ *
+ * For the levels listed in the example above, to select "plpd_optimized" for
+ * XGMI and "soc_pstate_2" for soc pstate policy -
+ *
+ * .. code-block:: console
+ *
+ *	echo "2" > /sys/bus/pci/devices/.../pm_policy/xgmi_plpd
+ *	echo "3" > /sys/bus/pci/devices/.../pm_policy/soc_pstate
+ *
+ */
 static ssize_t amdgpu_get_pm_policy_attr(struct device *dev,
 					 struct device_attribute *attr,
 					 char *buf)