drm/msm/mdp5: add tracking for clk enable-count

Accessing registers for an unclocked block is an insta-reboot on
snapdragon devices.  So add a bit of logic to track the enable_count so
we can WARN_ON() unclocked register writes.  This makes it much easier
to track down mistakes.
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/mdp/mdp5/mdp5_kms.c

@@ -249,6 +249,9 @@ int mdp5_disable(struct mdp5_kms *mdp5_kms)
 {
 	DBG("");
 
+	mdp5_kms->enable_count--;
+	WARN_ON(mdp5_kms->enable_count < 0);
+
 	clk_disable_unprepare(mdp5_kms->ahb_clk);
 	clk_disable_unprepare(mdp5_kms->axi_clk);
 	clk_disable_unprepare(mdp5_kms->core_clk);
@@ -262,6 +265,8 @@ int mdp5_enable(struct mdp5_kms *mdp5_kms)
 {
 	DBG("");
 
+	mdp5_kms->enable_count++;
+
 	clk_prepare_enable(mdp5_kms->ahb_clk);
 	clk_prepare_enable(mdp5_kms->axi_clk);
 	clk_prepare_enable(mdp5_kms->core_clk);

drivers/gpu/drm/msm/mdp/mdp5/mdp5_kms.h

@@ -76,6 +76,8 @@ struct mdp5_kms {
 	bool rpm_enabled;
 
 	struct mdp_irq error_handler;
+
+	int enable_count;
 };
 #define to_mdp5_kms(x) container_of(x, struct mdp5_kms, base)
 
@@ -167,11 +169,13 @@ struct mdp5_encoder {
 
 static inline void mdp5_write(struct mdp5_kms *mdp5_kms, u32 reg, u32 data)
 {
+	WARN_ON(mdp5_kms->enable_count <= 0);
 	msm_writel(data, mdp5_kms->mmio + reg);
 }
 
 static inline u32 mdp5_read(struct mdp5_kms *mdp5_kms, u32 reg)
 {
+	WARN_ON(mdp5_kms->enable_count <= 0);
 	return msm_readl(mdp5_kms->mmio + reg);
 }