Re: [PATCH 21/25] drm/tests: hdmi: Add HDMI 2.0 scrambling helpers coverage

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] drm/tests: hdmi: drm_connector_hdmi_enable_scrambling() SCDC
  check fails
--

commit 352379847f7c6ceae1ef1736d628408794656e3d
Author: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>

drm/tests: hdmi: Add HDMI 2.0 scrambling helpers coverage

This commit adds KUnit tests and a fake SCDC DDC adapter to cover the HDMI
2.0 scrambling helpers and SCDC status monitoring work.

> 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 294be8f4a3076..46654d8fa45cf 100644
> --- a/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c
> +++ b/drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c

[ ... ]

> +/*
> + * Test that enabling scrambling for a mode that doesn't need it leaves the
> + * source alone, but clears any stale scrambling setup on the sink side.
> + */
> +static void drm_test_hdmi_scrambling_enable_not_needed(struct kunit *test)
> +{
> +	struct drm_atomic_helper_connector_hdmi_priv *priv;
> +	struct drm_connector_state *conn_state;
> +	struct drm_connector *conn;
> +	int ret;
> +
> +	priv = drm_kunit_helper_connector_hdmi_init_with_scdc(test,
> +				&scdc_connector_hdmi_funcs,
> +				test_edid_hdmi_4k_rgb_yuv420_dc_max_600mhz);
> +	KUNIT_ASSERT_NOT_NULL(test, priv);
> +
> +	conn = &priv->connector;
> +	KUNIT_ASSERT_TRUE(test, conn->display_info.hdmi.scdc.scrambling.supported);
> +
> +	conn_state = kunit_kzalloc(test, sizeof(*conn_state), GFP_KERNEL);
> +	KUNIT_ASSERT_NOT_NULL(test, conn_state);
> +
> +	conn_state->hdmi.scrambler_needed = false;
> +
> +	priv->scdc_regs[SCDC_TMDS_CONFIG] = SCDC_TMDS_CONFIG_SCRAMBLED;
> +
> +	ret = drm_connector_hdmi_enable_scrambling(conn, conn_state);
> +	KUNIT_EXPECT_EQ(test, ret, 0);
> +
> +	KUNIT_EXPECT_EQ(test, priv->scdc_regs[SCDC_TMDS_CONFIG], 0);

[Severity: Medium]
Does this KUNIT_EXPECT_EQ() on priv->scdc_regs[SCDC_TMDS_CONFIG] always
fail?

drivers/gpu/drm/display/drm_hdmi_helper.c:drm_connector_hdmi_enable_scrambling() {
    ...
	if (!conn_state->hdmi.scrambler_needed)
		return 0;
    ...
}

When conn_state->hdmi.scrambler_needed is false,
drm_connector_hdmi_enable_scrambling() returns 0 immediately without
touching SCDC, so priv->scdc_regs[SCDC_TMDS_CONFIG] stays at
SCDC_TMDS_CONFIG_SCRAMBLED and drm_test_hdmi_scrambling_enable_not_needed()
fails on every run.  The commit message also claims that enabling
scrambling for a mode not needing it clears stale sink scrambling setup.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261114-drm-conn-hdmi-cleanup-v1-0-20e8a33a2286@collabora.com?part=21