drm/vc4: hdmi: Avoid hang with debug registers when suspended

[ Upstream commit 223ee25 ]

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.

Fixes: 25eb441 ("drm/vc4: hdmi: Add all the vc5 HDMI registers into the debugfs dumps")
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240621152055.4180873-17-dave.stevenson@raspberrypi.com
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: popcornmix

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -147,6 +147,8 @@ static int vc4_hdmi_debugfs_regs(struct seq_file *m, void *unused)
 	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);
@@ -156,6 +158,8 @@ static int vc4_hdmi_debugfs_regs(struct seq_file *m, void *unused)
 	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;