Provide test to verify a forced fallback to YUV420 output cannot succeed
when driver doesn't advertise YUV420 support.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
---
 drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c | 46 ++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c b/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
index 99bedb2d6f555b3b140256000dfa7491d2a8f515..c2976b42aa2aacd2a68a871bffe97e795ca713d4 100644
--- a/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
+++ b/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
@@ -1493,6 +1493,51 @@ static void drm_test_check_max_tmds_rate_format_fallback_yuv420(struct kunit *te
 	drm_modeset_acquire_fini(&ctx);
 }
 
+/*
+ * Test that if a driver supports only RGB, but the chosen mode can be
+ * supported by the screen only in YUV420 output format, we end up with
+ * an unsuccessful forced fallback attempt.
+ */
+static void drm_test_check_driver_unsupported_fallback_yuv420(struct kunit *test)
+{
+	struct drm_atomic_helper_connector_hdmi_priv *priv;
+	struct drm_modeset_acquire_ctx ctx;
+	struct drm_display_info *info;
+	struct drm_display_mode *yuv420_only_mode;
+	struct drm_connector *conn;
+	struct drm_device *drm;
+	struct drm_crtc *crtc;
+	int ret;
+
+	priv = drm_kunit_helper_connector_hdmi_init_with_edid(test,
+				BIT(HDMI_COLORSPACE_RGB),
+				12,
+				test_edid_hdmi_1080p_rgb_yuv_4k_yuv420_dc_max_200mhz);
+	KUNIT_ASSERT_NOT_NULL(test, priv);
+
+	drm = &priv->drm;
+	crtc = priv->crtc;
+	conn = &priv->connector;
+	info = &conn->display_info;
+	KUNIT_ASSERT_TRUE(test, info->is_hdmi);
+	KUNIT_ASSERT_FALSE(test, conn->ycbcr_420_allowed);
+
+	yuv420_only_mode = drm_kunit_display_mode_from_cea_vic(test, drm, 95);
+	KUNIT_ASSERT_NOT_NULL(test, yuv420_only_mode);
+	KUNIT_ASSERT_TRUE(test, drm_mode_is_420_only(info, yuv420_only_mode));
+
+	drm_modeset_acquire_init(&ctx, 0);
+
+	ret = drm_kunit_helper_enable_crtc_connector(test, drm,
+						     crtc, conn,
+						     yuv420_only_mode,
+						     &ctx);
+	KUNIT_EXPECT_LT(test, ret, 0);
+
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+}
+
 /*
  * Test that if a driver and screen supports RGB and YUV formats, and we
  * try to set the VIC 1 mode, we end up with 8bpc RGB even if we could
@@ -1884,6 +1929,7 @@ static struct kunit_case drm_atomic_helper_connector_hdmi_check_tests[] = {
 	KUNIT_CASE(drm_test_check_max_tmds_rate_bpc_fallback_yuv420),
 	KUNIT_CASE(drm_test_check_max_tmds_rate_format_fallback_yuv422),
 	KUNIT_CASE(drm_test_check_max_tmds_rate_format_fallback_yuv420),
+	KUNIT_CASE(drm_test_check_driver_unsupported_fallback_yuv420),
 	KUNIT_CASE(drm_test_check_output_bpc_crtc_mode_changed),
 	KUNIT_CASE(drm_test_check_output_bpc_crtc_mode_not_changed),
 	KUNIT_CASE(drm_test_check_output_bpc_dvi),

-- 
2.49.0

Hi,

On Wed, Mar 26, 2025 at 12:20:04PM +0200, Cristian Ciocaltea wrote:
> Provide test to verify a forced fallback to YUV420 output cannot succeed
> when driver doesn't advertise YUV420 support.
> 
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> ---
>  drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c | 46 ++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c b/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
> index 99bedb2d6f555b3b140256000dfa7491d2a8f515..c2976b42aa2aacd2a68a871bffe97e795ca713d4 100644
> --- a/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
> +++ b/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
> @@ -1493,6 +1493,51 @@ static void drm_test_check_max_tmds_rate_format_fallback_yuv420(struct kunit *te
>  	drm_modeset_acquire_fini(&ctx);
>  }
>  
> +/*
> + * Test that if a driver supports only RGB, but the chosen mode can be
> + * supported by the screen only in YUV420 output format, we end up with
> + * an unsuccessful forced fallback attempt.

What do you mean by "forced"?

> + */
> +static void drm_test_check_driver_unsupported_fallback_yuv420(struct kunit *test)
> +{
> +	struct drm_atomic_helper_connector_hdmi_priv *priv;
> +	struct drm_modeset_acquire_ctx ctx;
> +	struct drm_display_info *info;
> +	struct drm_display_mode *yuv420_only_mode;
> +	struct drm_connector *conn;
> +	struct drm_device *drm;
> +	struct drm_crtc *crtc;
> +	int ret;
> +
> +	priv = drm_kunit_helper_connector_hdmi_init_with_edid(test,
> +				BIT(HDMI_COLORSPACE_RGB),
> +				12,
> +				test_edid_hdmi_1080p_rgb_yuv_4k_yuv420_dc_max_200mhz);
> +	KUNIT_ASSERT_NOT_NULL(test, priv);
> +
> +	drm = &priv->drm;
> +	crtc = priv->crtc;
> +	conn = &priv->connector;
> +	info = &conn->display_info;
> +	KUNIT_ASSERT_TRUE(test, info->is_hdmi);
> +	KUNIT_ASSERT_FALSE(test, conn->ycbcr_420_allowed);
> +
> +	yuv420_only_mode = drm_kunit_display_mode_from_cea_vic(test, drm, 95);
> +	KUNIT_ASSERT_NOT_NULL(test, yuv420_only_mode);
> +	KUNIT_ASSERT_TRUE(test, drm_mode_is_420_only(info, yuv420_only_mode));
> +
> +	drm_modeset_acquire_init(&ctx, 0);
> +
> +	ret = drm_kunit_helper_enable_crtc_connector(test, drm,
> +						     crtc, conn,
> +						     yuv420_only_mode,
> +						     &ctx);
> +	KUNIT_EXPECT_LT(test, ret, 0);

I think that's where your current approach falls a bit short. You should
really craft the state yourself and check the returned value of
drm_atomic_check_only(), not rely on
drm_kunit_helper_enable_crtc_connector() doing the right thing, when it
doesn't really tell you :)

> +	drm_modeset_drop_locks(&ctx);
> +	drm_modeset_acquire_fini(&ctx);
> +}
> +

We still need to do the same with a driver that supports both, but the
monitor doesn't.

Maxime

On 4/10/25 12:21 PM, Maxime Ripard wrote:
> Hi,
> 
> On Wed, Mar 26, 2025 at 12:20:04PM +0200, Cristian Ciocaltea wrote:
>> Provide test to verify a forced fallback to YUV420 output cannot succeed
>> when driver doesn't advertise YUV420 support.
>>
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
>> ---
>>  drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c | 46 ++++++++++++++++++++++
>>  1 file changed, 46 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c b/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
>> index 99bedb2d6f555b3b140256000dfa7491d2a8f515..c2976b42aa2aacd2a68a871bffe97e795ca713d4 100644
>> --- a/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
>> +++ b/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
>> @@ -1493,6 +1493,51 @@ static void drm_test_check_max_tmds_rate_format_fallback_yuv420(struct kunit *te
>>  	drm_modeset_acquire_fini(&ctx);
>>  }
>>  
>> +/*
>> + * Test that if a driver supports only RGB, but the chosen mode can be
>> + * supported by the screen only in YUV420 output format, we end up with
>> + * an unsuccessful forced fallback attempt.
> 
> What do you mean by "forced"?

I wanted to describe the context where there's no alternative other than
doing the fallback.  Should we replace with "mandatory" maybe?

>> + */
>> +static void drm_test_check_driver_unsupported_fallback_yuv420(struct kunit *test)
>> +{
>> +	struct drm_atomic_helper_connector_hdmi_priv *priv;
>> +	struct drm_modeset_acquire_ctx ctx;
>> +	struct drm_display_info *info;
>> +	struct drm_display_mode *yuv420_only_mode;
>> +	struct drm_connector *conn;
>> +	struct drm_device *drm;
>> +	struct drm_crtc *crtc;
>> +	int ret;
>> +
>> +	priv = drm_kunit_helper_connector_hdmi_init_with_edid(test,
>> +				BIT(HDMI_COLORSPACE_RGB),
>> +				12,
>> +				test_edid_hdmi_1080p_rgb_yuv_4k_yuv420_dc_max_200mhz);
>> +	KUNIT_ASSERT_NOT_NULL(test, priv);
>> +
>> +	drm = &priv->drm;
>> +	crtc = priv->crtc;
>> +	conn = &priv->connector;
>> +	info = &conn->display_info;
>> +	KUNIT_ASSERT_TRUE(test, info->is_hdmi);
>> +	KUNIT_ASSERT_FALSE(test, conn->ycbcr_420_allowed);
>> +
>> +	yuv420_only_mode = drm_kunit_display_mode_from_cea_vic(test, drm, 95);
>> +	KUNIT_ASSERT_NOT_NULL(test, yuv420_only_mode);
>> +	KUNIT_ASSERT_TRUE(test, drm_mode_is_420_only(info, yuv420_only_mode));
>> +
>> +	drm_modeset_acquire_init(&ctx, 0);
>> +
>> +	ret = drm_kunit_helper_enable_crtc_connector(test, drm,
>> +						     crtc, conn,
>> +						     yuv420_only_mode,
>> +						     &ctx);
>> +	KUNIT_EXPECT_LT(test, ret, 0);
> 
> I think that's where your current approach falls a bit short. You should
> really craft the state yourself and check the returned value of
> drm_atomic_check_only(), not rely on
> drm_kunit_helper_enable_crtc_connector() doing the right thing, when it
> doesn't really tell you :)

Ack.

> 
>> +	drm_modeset_drop_locks(&ctx);
>> +	drm_modeset_acquire_fini(&ctx);
>> +}
>> +
> 
> We still need to do the same with a driver that supports both, but the
> monitor doesn't.

Ack.

Thanks,
Cristian