[PATCH v2 16/31] drm/vc4: hdmi: Avoid hang with debug registers when suspended

[Dave Stevenson]

From: Dom Cobley <popcornmix at gmail.com>

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: 25eb441d55d4 ("drm/vc4: hdmi: Add all the vc5 HDMI registers into the debugfs dumps")
Signed-off-by: Dom Cobley <popcornmix at gmail.com>
Signed-off-by: Dave Stevenson <dave.stevenson at raspberrypi.com>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index ad88915306f1..680e40a688a5 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/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;
-- 
2.34.1