[PATCH v4] drm/bridge: dw-hdmi-qp: Guard clear_audio_infoframe when PHY is down

[Frank Zhang <rmxpzlb@gmail.com>]

The following panic was observed during system reboot:

Kernel panic - not syncing: Asynchronous SError Interrupt
CPU: 6 UID: 1000 PID: 2348 Comm: pipewire ... 7.0.5+ #4 PREEMPT(full)
Call trace:
 ...
 regmap_update_bits_base+0x70/0xa8
 dw_hdmi_qp_bridge_clear_audio_infoframe+0x3c/0x58 [dw_hdmi_qp]
 drm_bridge_connector_clear_audio_infoframe+0x2c/0x48 [drm_display_helper]
 ...
 dw_hdmi_qp_audio_disable+0x28/0xa8 [dw_hdmi_qp]
 drm_bridge_connector_audio_shutdown+0x38/0x68 [drm_display_helper]
 drm_connector_hdmi_audio_shutdown+0x28/0x40 [drm_display_helper]
 hdmi_codec_shutdown+0x60/0x90 [snd_soc_hdmi_codec]
 ...
 snd_pcm_release_substream+0xcc/0x120 [snd_pcm]
 snd_pcm_release+0x4c/0xc0 [snd_pcm]
 ...

The root cause is pipewire tries to close the HDMI audio device after
atomic_disable(), which sets tmds_char_rate to 0 and disables the PHY.

In this case, dw_hdmi_qp_audio_disable() will call
dw_hdmi_qp_bridge_clear_audio_infoframe(), accessing register without
checking tmds_char_rate.

Add a tmds_char_rate guard in dw_hdmi_qp_bridge_clear_audio_infoframe().
Decouple write_audio_infoframe from clear_audio_infoframe to avoid the
redundant check in the write path.
Add PKTSCHED_AMD_TX_EN to the clear mask to keep the enable/disable
balance.

Fixes: fd0141d1a8a2 ("drm/bridge: synopsys: Add audio support for dw-hdmi-qp")
Cc: stable@vger.kernel.org
Signed-off-by: Frank Zhang <rmxpzlb@gmail.com>

---
Changes in v2:
- Move drm_atomic_helper_connector_hdmi_clear_audio_infoframe() inside
  the if (hdmi->tmds_char_rate) of dw_hdmi_qp_audio_disable().
- Link to v1: https://lore.kernel.org/all/20260416093150.13853-1-rmxpzlb@gmail.com/

Changes in v3:
- Add a tmds_char_rate guard in clear_audio_infoframe path.
- Decouple write_audio_infoframe from clear_audio_infoframe.
- Balance the PKTSCHED_AMD_TX_EN bit enable/disable.
- Link to v2: https://lore.kernel.org/all/20260418101936.7731-1-rmxpzlb@gmail.com/

Changes in v4:
- Update panic stack on 7.0.5
- Link to v3: https://lore.kernel.org/all/20260423081514.15444-1-rmxpzlb@gmail.com/
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
index d649a1cf07f5..1c18f8650fcd 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
@@ -886,11 +886,11 @@ static int dw_hdmi_qp_bridge_clear_audio_infoframe(struct drm_bridge *bridge)
 {
 	struct dw_hdmi_qp *hdmi = bridge->driver_private;
 
-	dw_hdmi_qp_mod(hdmi, 0,
-		       PKTSCHED_ACR_TX_EN |
-		       PKTSCHED_AUDS_TX_EN |
-		       PKTSCHED_AUDI_TX_EN,
-		       PKTSCHED_PKT_EN);
+	if (hdmi->tmds_char_rate)
+		dw_hdmi_qp_mod(hdmi, 0,
+			       PKTSCHED_ACR_TX_EN | PKTSCHED_AMD_TX_EN |
+			       PKTSCHED_AUDS_TX_EN | PKTSCHED_AUDI_TX_EN,
+			       PKTSCHED_PKT_EN);
 
 	return 0;
 }
@@ -989,7 +989,10 @@ static int dw_hdmi_qp_bridge_write_audio_infoframe(struct drm_bridge *bridge,
 {
 	struct dw_hdmi_qp *hdmi = bridge->driver_private;
 
-	dw_hdmi_qp_bridge_clear_audio_infoframe(bridge);
+	dw_hdmi_qp_mod(hdmi, 0,
+		       PKTSCHED_ACR_TX_EN | PKTSCHED_AMD_TX_EN |
+		       PKTSCHED_AUDS_TX_EN | PKTSCHED_AUDI_TX_EN,
+		       PKTSCHED_PKT_EN);
 
 	/*
 	 * AUDI_CONTENTS0: { RSV, HB2, HB1, RSV }
-- 
2.54.0