drm/i915: tame the chattermouth (v2)

Many distro's have mechanism in place to collect and automatically file
bugs for failed WARN()s.  And since i915 has a lot of hw state sanity
checks which result in WARN(), it generates quite a lot of noise which
is somewhat disconcerting to the end user.

Separate out the internal hw-is-in-the-state-I-expected checks into
I915_STATE_WARN()s and allow configuration via i915.verbose_checks module
param about whether this will generate a full blown stacktrace or just
DRM_ERROR().  The new moduleparam defaults to true, so by default there
is no change in behavior.  And even when disabled, you will still get
an error message logged.

v2: paint the macro names blue, clarify that the default behavior
    remains the same as before

Signed-off-by: Rob Clark <robdclark@gmail.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -72,6 +72,35 @@
 #define MISSING_CASE(x) WARN(1, "Missing switch case (%lu) in %s\n", \
 			     (long) (x), __func__);
 
+/* Use I915_STATE_WARN(x) and I915_STATE_WARN_ON() (rather than WARN() and
+ * WARN_ON()) for hw state sanity checks to check for unexpected conditions
+ * which may not necessarily be a user visible problem.  This will either
+ * WARN() or DRM_ERROR() depending on the verbose_checks moduleparam, to
+ * enable distros and users to tailor their preferred amount of i915 abrt
+ * spam.
+ */
+#define I915_STATE_WARN(condition, format...) ({			\
+	int __ret_warn_on = !!(condition);				\
+	if (unlikely(__ret_warn_on)) {					\
+		if (i915.verbose_state_checks)				\
+			__WARN_printf(format);				\
+		else 							\
+			DRM_ERROR(format);				\
+	}								\
+	unlikely(__ret_warn_on);					\
+})
+
+#define I915_STATE_WARN_ON(condition) ({				\
+	int __ret_warn_on = !!(condition);				\
+	if (unlikely(__ret_warn_on)) {					\
+		if (i915.verbose_state_checks)				\
+			__WARN_printf("WARN_ON(" #condition ")\n");	\
+		else 							\
+			DRM_ERROR("WARN_ON(" #condition ")\n");		\
+	}								\
+	unlikely(__ret_warn_on);					\
+})
+
 enum pipe {
 	INVALID_PIPE = -1,
 	PIPE_A = 0,
@@ -2401,6 +2430,7 @@ struct i915_params {
 	bool disable_vtd_wa;
 	int use_mmio_flip;
 	bool mmio_debug;
+	bool verbose_state_checks;
 };
 extern struct i915_params i915 __read_mostly;
 

drivers/gpu/drm/i915/i915_params.c

@@ -51,6 +51,7 @@ struct i915_params i915 __read_mostly = {
 	.disable_vtd_wa = 0,
 	.use_mmio_flip = 0,
 	.mmio_debug = 0,
+	.verbose_state_checks = 1,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -173,3 +174,7 @@ module_param_named(mmio_debug, i915.mmio_debug, bool, 0600);
 MODULE_PARM_DESC(mmio_debug,
 	"Enable the MMIO debug code (default: false). This may negatively "
 	"affect performance.");
+
+module_param_named(verbose_state_checks, i915.verbose_state_checks, bool, 0600);
+MODULE_PARM_DESC(verbose_state_checks,
+	"Enable verbose logs (ie. WARN_ON()) in case of unexpected hw state conditions.");