From e5e7679d634b10e88df340c85cd8368c9f9989eb Mon Sep 17 00:00:00 2001
From: Dom Cobley <popcornmix@gmail.com>
Date: Tue, 5 Sep 2023 19:38:24 +0100
Subject: [PATCH] drm/vc4: hdmi: Avoid hang with debug registers when suspended

Trying to read /sys/kernel/debug/dri/1/hdmi1_regs
when the hdmi is disconnected results in a fatal system hang.

This is due to the pm suspend code disabling the dvp clock.
That is just a gate of the 108MHz clock in DVP_HT_RPI_MISC_CONFIG,
which results in accesses hanging AXI bus.

Protect against this.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -193,6 +193,8 @@ static int vc4_hdmi_debugfs_regs(struct
 	if (!drm_dev_enter(drm, &idx))
 		return -ENODEV;
 
+	WARN_ON(pm_runtime_resume_and_get(&vc4_hdmi->pdev->dev));
+
 	drm_print_regset32(&p, &vc4_hdmi->hdmi_regset);
 	drm_print_regset32(&p, &vc4_hdmi->hd_regset);
 	drm_print_regset32(&p, &vc4_hdmi->cec_regset);
@@ -202,6 +204,8 @@ static int vc4_hdmi_debugfs_regs(struct
 	drm_print_regset32(&p, &vc4_hdmi->ram_regset);
 	drm_print_regset32(&p, &vc4_hdmi->rm_regset);
 
+	pm_runtime_put(&vc4_hdmi->pdev->dev);
+
 	drm_dev_exit(idx);
 
 	return 0;
