drm/i915: Redefine EINVAL for debugging

To aide debugging spurious EINVALs, include a debug message every time
we emit one from execbuf.

References: https://bugs.freedesktop.org/show_bug.cgi?id=106744
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180621080150.8110-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -66,6 +66,15 @@ enum {
 #define __I915_EXEC_ILLEGAL_FLAGS \
 	(__I915_EXEC_UNKNOWN_FLAGS | I915_EXEC_CONSTANTS_MASK)
 
+/* Catch emission of unexpected errors for CI! */
+#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
+#undef EINVAL
+#define EINVAL ({ \
+	DRM_DEBUG_DRIVER("EINVAL at %s:%d\n", __func__, __LINE__); \
+	22; \
+})
+#endif
+
 /**
  * DOC: User command execution
  *