drm/amd/display: Add backlight pwm debugfs

[Why]
ABM enablement testing can be automated if a way of reading
target and current hardware backlight is available

[How]
Expand debugfs interface with two new entries.
Hook directly into dc interface.  Units are as
a fraction of 0x1000 = 100%

Use the built-in amdgpu function for creating
read-only debugfs files
Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -783,6 +783,45 @@ static ssize_t dtn_log_write(
 	return size;
 }
 
+/*
+ * Backlight at this moment.  Read only.
+ * As written to display, taking ABM and backlight lut into account.
+ * Ranges from 0x0 to 0x10000 (= 100% PWM)
+ */
+static int current_backlight_read(struct seq_file *m, void *data)
+{
+	struct drm_info_node *node = (struct drm_info_node *)m->private;
+	struct drm_device *dev = node->minor->dev;
+	struct amdgpu_device *adev = dev->dev_private;
+	struct dc *dc = adev->dm.dc;
+	unsigned int backlight = dc_get_current_backlight_pwm(dc);
+
+	seq_printf(m, "0x%x\n", backlight);
+	return 0;
+}
+
+/*
+ * Backlight value that is being approached.  Read only.
+ * As written to display, taking ABM and backlight lut into account.
+ * Ranges from 0x0 to 0x10000 (= 100% PWM)
+ */
+static int target_backlight_read(struct seq_file *m, void *data)
+{
+	struct drm_info_node *node = (struct drm_info_node *)m->private;
+	struct drm_device *dev = node->minor->dev;
+	struct amdgpu_device *adev = dev->dev_private;
+	struct dc *dc = adev->dm.dc;
+	unsigned int backlight = dc_get_target_backlight_pwm(dc);
+
+	seq_printf(m, "0x%x\n", backlight);
+	return 0;
+}
+
+static const struct drm_info_list amdgpu_dm_debugfs_list[] = {
+	{"amdgpu_current_backlight_pwm", &current_backlight_read},
+	{"amdgpu_target_backlight_pwm", &target_backlight_read},
+};
+
 int dtn_debugfs_init(struct amdgpu_device *adev)
 {
 	static const struct file_operations dtn_log_fops = {
@@ -793,9 +832,15 @@ int dtn_debugfs_init(struct amdgpu_device *adev)
 	};
 
 	struct drm_minor *minor = adev->ddev->primary;
-	struct dentry *root = minor->debugfs_root;
+	struct dentry *ent, *root = minor->debugfs_root;
+	int ret;
+
+	ret = amdgpu_debugfs_add_files(adev, amdgpu_dm_debugfs_list,
+				ARRAY_SIZE(amdgpu_dm_debugfs_list));
+	if (ret)
+		return ret;
 
-	struct dentry *ent = debugfs_create_file(
+	ent = debugfs_create_file(
 		"amdgpu_dm_dtn_log",
 		0644,
 		root,

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -1779,6 +1779,26 @@ void dc_resume(struct dc *dc)
 		core_link_resume(dc->links[i]);
 }
 
+unsigned int dc_get_current_backlight_pwm(struct dc *dc)
+{
+	struct abm *abm = dc->res_pool->abm;
+
+	if (abm)
+		return abm->funcs->get_current_backlight(abm);
+
+	return 0;
+}
+
+unsigned int dc_get_target_backlight_pwm(struct dc *dc)
+{
+	struct abm *abm = dc->res_pool->abm;
+
+	if (abm)
+		return abm->funcs->get_target_backlight(abm);
+
+	return 0;
+}
+
 bool dc_is_dmcu_initialized(struct dc *dc)
 {
 	struct dmcu *dmcu = dc->res_pool->dmcu;

drivers/gpu/drm/amd/display/dc/dc.h

@@ -749,6 +749,9 @@ void dc_set_power_state(
 		struct dc *dc,
 		enum dc_acpi_cm_power_state power_state);
 void dc_resume(struct dc *dc);
+unsigned int dc_get_current_backlight_pwm(struct dc *dc);
+unsigned int dc_get_target_backlight_pwm(struct dc *dc);
+
 bool dc_is_dmcu_initialized(struct dc *dc);
 
 #endif /* DC_INTERFACE_H_ */