linux-kernel - [PATCH 5.19 0422/1157] drm/vc4: hdmi: Force modeset when bpc or format changes

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Message-Id: <20220815180456.543086316@linuxfoundation.org>
Date:   Mon, 15 Aug 2022 19:56:18 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dom Cobley <popcornmix@...il.com>,
        Maxime Ripard <maxime@...no.tech>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.19 0422/1157] drm/vc4: hdmi: Force modeset when bpc or format changes

From: Dom Cobley <popcornmix@...il.com>

[ Upstream commit c94cd0620a922156c9ff9af9c3301b174b287677 ]

Whenever the maximum BPC is changed, vc4_hdmi_encoder_compute_config()
might pick up a different BPC or format depending on the display
capabilities.

That change will have a number of side effects, including the clock
rates and whether the scrambling is enabled.

However, only drm_crtc_state.connectors_changed will be set to true,
since that properly only affects the connector.

This means that while drm_atomic_crtc_needs_modeset() will return true,
and thus drm_atomic_helper_commit_modeset_enables() will call our
encoder atomic_enable() hook, mode_changed will be false.

So crtc_set_mode() will not call our encoder .atomic_mode_set() hook. We
use this hook in vc4 to set the vc4_hdmi_connector_state.output_bpc (and
output_format), and will then reuse the value in .atomic_enable() to select
whether or not scrambling should be enabled.

However, since our clock rate is pre-computed during .atomic_check(), we
end up with the clocks properly configured, but the scrambling disabled,
leading to a blank screen.

Let's set mode_changed to true in our HDMI driver to force the update of
output_bpc, and thus prevent the issue entirely.

Fixes: ba8c0faebbb0 ("drm/vc4: hdmi: Enable 10/12 bpc output")
Signed-off-by: Dom Cobley <popcornmix@...il.com>
Link: https://lore.kernel.org/r/20220613144800.326124-32-maxime@cerno.tech
Signed-off-by: Maxime Ripard <maxime@...no.tech>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 674bd29a7cf2..3829e13c8627 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -1620,9 +1620,14 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
 					 struct drm_crtc_state *crtc_state,
 					 struct drm_connector_state *conn_state)
 {
+	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
+	struct drm_connector *connector = &vc4_hdmi->connector;
+	struct drm_connector_state *old_conn_state =
+		drm_atomic_get_old_connector_state(conn_state->state, connector);
+	struct vc4_hdmi_connector_state *old_vc4_state =
+		conn_state_to_vc4_hdmi_conn_state(old_conn_state);
 	struct vc4_hdmi_connector_state *vc4_state = conn_state_to_vc4_hdmi_conn_state(conn_state);
 	struct drm_display_mode *mode = &crtc_state->adjusted_mode;
-	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
 	unsigned long long tmds_char_rate = mode->clock * 1000;
 	unsigned long long tmds_bit_rate;
 	int ret;
@@ -1651,6 +1656,11 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
 	if (ret)
 		return ret;

+	/* vc4_hdmi_encoder_compute_config may have changed output_bpc and/or output_format */
+	if (vc4_state->output_bpc != old_vc4_state->output_bpc ||
+	    vc4_state->output_format != old_vc4_state->output_format)
+		crtc_state->mode_changed = true;
+
 	return 0;
 }

-- 
2.35.1