[PATCH v3 1/3] drm/vc4: hdmi: power down the BCM2712 PHY when the output is disabled

[Lucas Tanure <lucas.tanure@neat.no>]

From: Dom Cobley <popcornmix@gmail.com>

vc6_hdmi_phy_disable() is empty, so on BCM2712 the PHY keeps its PLL
and TMDS drivers running after the HDMI output is disabled, until the
next vc6_hdmi_phy_init(). The TMDS clock is therefore not stopped
between two mode sets, which the SCDC clock ratio change requires, and
the idle PHY wastes power.

Reset and power down the PHY on disable, as the BCM2711 variant does.

Fixes: 0b1dbe82e051 ("drm/vc4: hdmi: Add support for BCM2712 HDMI controllers")
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
[lucas.tanure: Rewrote commit message to clarify the issue and fix]
Signed-off-by: Lucas Tanure <lucas.tanure@neat.no>
---
 drivers/gpu/drm/vc4/vc4_hdmi_phy.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi_phy.c b/drivers/gpu/drm/vc4/vc4_hdmi_phy.c
index 56e6a35da357..5040f014bf7e 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi_phy.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi_phy.c
@@ -1197,4 +1197,9 @@ void vc6_hdmi_phy_init(struct vc4_hdmi *vc4_hdmi,
 
 void vc6_hdmi_phy_disable(struct vc4_hdmi *vc4_hdmi)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&vc4_hdmi->hw_lock, flags);
+	vc6_hdmi_reset_phy(vc4_hdmi);
+	spin_unlock_irqrestore(&vc4_hdmi->hw_lock, flags);
 }
-- 
2.56.0