drm/amd/display: Test backlight level readback path

[WHAT]
Add KUnit coverage for the backlight level read path.

A faked link_service vtable returns canned PWM and AUX brightness values,
letting the tests verify both the successful readback and the
DC_ERROR/AUX-failure fallbacks to the cached brightness, plus the
get_brightness() device-index wrapper.

Assisted-by: Copilot:Claude-Opus-4.8
Reviewed-by: Bhawanpreet Lakha <bhawanpreet.lakha@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

3 files changed, 164 insertions, 3 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c
index d35b90912bd2..452e772ef136 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c
@@ -362,8 +362,8 @@ int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 }
 EXPORT_IF_KUNIT(amdgpu_dm_backlight_update_status);
 
-static u32 amdgpu_dm_backlight_get_level(struct amdgpu_display_manager *dm,
-					 int bl_idx)
+STATIC_IFN_KUNIT
+u32 amdgpu_dm_backlight_get_level(struct amdgpu_display_manager *dm, int bl_idx)
 {
 	int ret;
 	struct amdgpu_dm_backlight_caps caps;
@@ -387,14 +387,17 @@ static u32 amdgpu_dm_backlight_get_level(struct amdgpu_display_manager *dm,
 
 	return convert_brightness_to_user(&caps, ret);
 }
+EXPORT_IF_KUNIT(amdgpu_dm_backlight_get_level);
 
-static int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd)
+STATIC_IFN_KUNIT
+int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd)
 {
 	struct amdgpu_display_manager *dm = bl_get_data(bd);
 	int i = amdgpu_dm_backlight_get_device_index(dm, bd);
 
 	return amdgpu_dm_backlight_get_level(dm, i);
 }
+EXPORT_IF_KUNIT(amdgpu_dm_backlight_get_brightness);
 
 static const struct backlight_ops amdgpu_dm_backlight_ops = {
 	.options = BL_CORE_SUSPENDRESUME,
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.h
index 5fbaf67369f1..7b417c79980f 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.h
@@ -54,6 +54,8 @@ extern const struct attribute_group amdgpu_group;
 struct dc_stream_state *dm_find_stream_with_link(struct amdgpu_display_manager *dm,
 						 struct dc_link *link);
 int amdgpu_dm_backlight_update_status(struct backlight_device *bd);
+u32 amdgpu_dm_backlight_get_level(struct amdgpu_display_manager *dm, int bl_idx);
+int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd);
 int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps,
 			 unsigned int *min, unsigned int *max);
 void convert_custom_brightness(const struct amdgpu_dm_backlight_caps *caps,
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c
index 732ac8db742d..10965306e29d 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/tests/amdgpu_dm_backlight_test.c
@@ -16,6 +16,7 @@
 #include "amdgpu_dm_backlight.h"
 #include "amdgpu_dm_kunit_test_helpers.h"
 #include "amd_shared.h"
+#include "link_service.h"
 #include "dc/inc/hw/panel_cntl.h"
 
 struct dm_backlight_connector_fixture {
@@ -290,6 +291,155 @@ static void dm_test_backlight_update_status_no_stream(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, dm->brightness[1], 3456U);
 }
 
+static void setup_test_link_service(struct kunit *test, struct dc_link *link)
+{
+	struct link_service *link_srv;
+	struct dc_context *ctx;
+	struct dc *dc;
+
+	dc = kunit_kzalloc(test, sizeof(*dc), GFP_KERNEL);
+	ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
+	link_srv = kunit_kzalloc(test, sizeof(*link_srv), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dc);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, link_srv);
+
+	dc->ctx = ctx;
+	dc->link_srv = link_srv;
+	ctx->dc = dc;
+	link->dc = dc;
+	link->ctx = ctx;
+}
+
+static int dm_test_get_backlight_level_mid(const struct dc_link *link)
+{
+	return (0x101 * AMDGPU_DM_DEFAULT_MIN_BACKLIGHT) + 1000;
+}
+
+static int dm_test_get_backlight_level_error(const struct dc_link *link)
+{
+	return DC_ERROR_UNEXPECTED;
+}
+
+static bool dm_test_get_backlight_level_nits(struct dc_link *link,
+					     uint32_t *avg,
+					     uint32_t *peak)
+{
+	*avg = 250000;
+	*peak = 300000;
+
+	return true;
+}
+
+static bool dm_test_get_backlight_level_nits_fail(struct dc_link *link,
+						  uint32_t *avg,
+						  uint32_t *peak)
+{
+	return false;
+}
+
+/* Tests for amdgpu_dm_backlight_get_level()/get_brightness() */
+
+/**
+ * dm_test_backlight_get_level_pwm_success - Test PWM brightness readback
+ * @test: The KUnit test context
+ */
+static void dm_test_backlight_get_level_pwm_success(struct kunit *test)
+{
+	struct amdgpu_display_manager *dm = dm_kunit_alloc_dm(test);
+	struct dc_link *link = dm_kunit_alloc_link(test);
+	u32 hw_level = dm_test_get_backlight_level_mid(link);
+
+	setup_test_link_service(test, link);
+	link->dc->link_srv->edp_get_backlight_level = dm_test_get_backlight_level_mid;
+	dm->backlight_link[0] = link;
+
+	KUNIT_EXPECT_EQ(test, amdgpu_dm_backlight_get_level(dm, 0),
+			 convert_brightness_to_user(&dm->backlight_caps[0], hw_level));
+}
+
+/**
+ * dm_test_backlight_get_level_pwm_error - Test PWM readback fallback
+ * @test: The KUnit test context
+ */
+static void dm_test_backlight_get_level_pwm_error(struct kunit *test)
+{
+	struct amdgpu_display_manager *dm = dm_kunit_alloc_dm(test);
+	struct dc_link *link = dm_kunit_alloc_link(test);
+
+	setup_test_link_service(test, link);
+	link->dc->link_srv->edp_get_backlight_level = dm_test_get_backlight_level_error;
+	dm->brightness[0] = 4321;
+	dm->backlight_link[0] = link;
+
+	KUNIT_EXPECT_EQ(test, amdgpu_dm_backlight_get_level(dm, 0), 4321U);
+}
+
+/**
+ * dm_test_backlight_get_level_aux_success - Test AUX brightness readback
+ * @test: The KUnit test context
+ */
+static void dm_test_backlight_get_level_aux_success(struct kunit *test)
+{
+	struct amdgpu_display_manager *dm = dm_kunit_alloc_dm(test);
+	struct dc_link *link = dm_kunit_alloc_link(test);
+	struct amdgpu_dm_backlight_caps *caps = &dm->backlight_caps[0];
+
+	setup_test_link_service(test, link);
+	link->dc->link_srv->edp_get_backlight_level_nits = dm_test_get_backlight_level_nits;
+	dm->backlight_link[0] = link;
+	caps->caps_valid = true;
+	caps->aux_support = true;
+	caps->aux_min_input_signal = 1;
+	caps->aux_max_input_signal = 512;
+
+	KUNIT_EXPECT_EQ(test, amdgpu_dm_backlight_get_level(dm, 0),
+			 convert_brightness_to_user(caps, 250000));
+}
+
+/**
+ * dm_test_backlight_get_level_aux_error - Test AUX readback fallback
+ * @test: The KUnit test context
+ */
+static void dm_test_backlight_get_level_aux_error(struct kunit *test)
+{
+	struct amdgpu_display_manager *dm = dm_kunit_alloc_dm(test);
+	struct dc_link *link = dm_kunit_alloc_link(test);
+	struct amdgpu_dm_backlight_caps *caps = &dm->backlight_caps[0];
+
+	setup_test_link_service(test, link);
+	link->dc->link_srv->edp_get_backlight_level_nits = dm_test_get_backlight_level_nits_fail;
+	dm->brightness[0] = 6789;
+	dm->backlight_link[0] = link;
+	caps->caps_valid = true;
+	caps->aux_support = true;
+
+	KUNIT_EXPECT_EQ(test, amdgpu_dm_backlight_get_level(dm, 0), 6789U);
+}
+
+/**
+ * dm_test_backlight_get_brightness_uses_device_index - Test get_brightness wrapper
+ * @test: The KUnit test context
+ */
+static void dm_test_backlight_get_brightness_uses_device_index(struct kunit *test)
+{
+	struct amdgpu_display_manager *dm = dm_kunit_alloc_dm(test);
+	struct dc_link *link = dm_kunit_alloc_link(test);
+	struct backlight_device *bd;
+
+	setup_test_link_service(test, link);
+	link->dc->link_srv->edp_get_backlight_level = dm_test_get_backlight_level_error;
+	bd = kunit_kzalloc(test, sizeof(*bd), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, bd);
+	dev_set_drvdata(&bd->dev, dm);
+	dm->num_of_edps = 2;
+	dm->backlight_dev[1] = bd;
+	dm->brightness[1] = 2468;
+	dm->backlight_link[1] = link;
+
+	KUNIT_EXPECT_EQ(test, amdgpu_dm_backlight_get_brightness(bd), 2468);
+}
+
 /* Tests for amdgpu_dm_backlight_get_device_index() */
 
 /**
@@ -1460,6 +1610,12 @@ static struct kunit_case dm_backlight_test_cases[] = {
 	KUNIT_CASE(dm_test_backlight_set_level_pwm_programs_power_module),
 	KUNIT_CASE(dm_test_backlight_set_level_reallows_idle),
 	KUNIT_CASE(dm_test_backlight_update_status_no_stream),
+	/* amdgpu_dm_backlight_get_level / get_brightness */
+	KUNIT_CASE(dm_test_backlight_get_level_pwm_success),
+	KUNIT_CASE(dm_test_backlight_get_level_pwm_error),
+	KUNIT_CASE(dm_test_backlight_get_level_aux_success),
+	KUNIT_CASE(dm_test_backlight_get_level_aux_error),
+	KUNIT_CASE(dm_test_backlight_get_brightness_uses_device_index),
 	/* amdgpu_dm_backlight_get_device_index */
 	KUNIT_CASE(dm_test_backlight_device_index_matches_second),
 	KUNIT_CASE(dm_test_backlight_device_index_missing_fallback),