drm/vc4: hdmi: Warn if we access the controller while disabled

We've had many silent hangs where the kernel would look like it just
stalled due to the access to one of the HDMI registers while the
controller was disabled.

Add a warning if we're about to do that so that it's at least not silent
anymore.

Reviewed-by: Dave Stevenson <[e-mail]>
Signed-off-by: Maxime Ripard <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/vc4/vc4_hdmi_regs.h

···
 #ifndef _VC4_HDMI_REGS_H_
 #define _VC4_HDMI_REGS_H_
 
+#include <linux/pm_runtime.h>
+
 #include "vc4_hdmi.h"
 
 #define VC4_HDMI_PACKET_STRIDE			0x24
···
 	const struct vc4_hdmi_variant *variant = hdmi->variant;
 	void __iomem *base;
 
+	WARN_ON(!pm_runtime_active(&hdmi->pdev->dev));
+
 	if (reg >= variant->num_registers) {
 		dev_warn(&hdmi->pdev->dev,
 			 "Invalid register ID %u\n", reg);
···
 	const struct vc4_hdmi_register *field;
 	const struct vc4_hdmi_variant *variant = hdmi->variant;
 	void __iomem *base;
+
+	WARN_ON(!pm_runtime_active(&hdmi->pdev->dev));
 
 	if (reg >= variant->num_registers) {
 		dev_warn(&hdmi->pdev->dev,