On eDP interfaces with no panel connected, panel-simple-dp-aux fails to
read DPCD over AUX during probe, leaving hpd_state at ST_DISCONNECTED.
msm_dp_bridge_atomic_enable() exits early as a result, so
msm_dp_display_enable() is never called and power_on remains false with
link clocks never enabled.

During system suspend, drm_atomic_helper_suspend() still invokes
atomic_disable() for all registered bridges. The resulting write to
REG_DP_STATE_CTRL against an unpowered controller triggers a NoC slave
error, causing a fatal crash.

Guard push_idle with a power_on check to skip the register access when the
display was never enabled.

Signed-off-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
---
 drivers/gpu/drm/msm/dp/dp_display.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index 1b3cbf4016ef..51b60eb9c2df 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -1660,6 +1660,13 @@ void msm_dp_bridge_atomic_disable(struct drm_bridge *drm_bridge,
 
 	msm_dp_display = container_of(dp, struct msm_dp_display_private, msm_dp_display);
 
+	/*
+	 * push_idle accesses link registers which require link clocks to be on.
+	 * Skip if the display was never powered on (e.g. eDP with no panel).
+	 */
+	if (!dp->power_on)
+		return;
+
 	msm_dp_ctrl_push_idle(msm_dp_display->ctrl);
 }
 

---
base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
change-id: 20260511-edp_suspend-0e45d0110633

Best regards,
-- 
Yongxing Mou <yongxing.mou@oss.qualcomm.com>

On Mon, May 11, 2026 at 04:36:03PM +0800, Yongxing Mou wrote:
> On eDP interfaces with no panel connected, panel-simple-dp-aux fails to
> read DPCD over AUX during probe, leaving hpd_state at ST_DISCONNECTED.
> msm_dp_bridge_atomic_enable() exits early as a result, so

Why is atomic_enable() called for disconnected bridge?

> msm_dp_display_enable() is never called and power_on remains false with
> link clocks never enabled.
> 
> During system suspend, drm_atomic_helper_suspend() still invokes
> atomic_disable() for all registered bridges. The resulting write to
> REG_DP_STATE_CTRL against an unpowered controller triggers a NoC slave
> error, causing a fatal crash.
> 
> Guard push_idle with a power_on check to skip the register access when the
> display was never enabled.
> 
> Signed-off-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>

Fixes?

> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 1b3cbf4016ef..51b60eb9c2df 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1660,6 +1660,13 @@ void msm_dp_bridge_atomic_disable(struct drm_bridge *drm_bridge,
>  
>  	msm_dp_display = container_of(dp, struct msm_dp_display_private, msm_dp_display);
>  
> +	/*
> +	 * push_idle accesses link registers which require link clocks to be on.
> +	 * Skip if the display was never powered on (e.g. eDP with no panel).
> +	 */
> +	if (!dp->power_on)
> +		return;
> +
>  	msm_dp_ctrl_push_idle(msm_dp_display->ctrl);
>  }
>  
> 
> ---
> base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
> change-id: 20260511-edp_suspend-0e45d0110633
> 
> Best regards,
> -- 
> Yongxing Mou <yongxing.mou@oss.qualcomm.com>
> 

-- 
With best wishes
Dmitry