[PATCH v3 1/4] drm: Define user readable error codes for atomic ioctl

[Arun R Murthy]

There can be multiple reasons for a failure in atomic_ioctl. Most often
in these error conditions -EINVAL is returned. User/Compositor would
have to blindly take a call on failure of this ioctl so as to use
ALLOW_MODESET or any. It would be good if user/compositor gets a
readable error code on failure so they can take proper corrections in
the next commit.
The struct drm_mode_atomic is being passed by the user/compositor which
holds the properties for modeset/flip. Reusing the same struct for
returning the error code in case of failure can save by creating a new
uapi/interface for returning the error code.
The element 'reserved' in the struct drm_mode_atomic is used for
returning the user readable error code. This points to the struct
drm_mode_atomic_err_code. Failure reasons have been initialized in
DRM_MODE_ATOMIC_FAILURE_REASON.

Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
 include/uapi/drm/drm_mode.h | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index a122bea2559387576150236e3a88f99c24ad3138..f0986a3fe9a7d61e57e9a9a5ec01a604343f6930 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -45,6 +45,7 @@ extern "C" {
 #define DRM_CONNECTOR_NAME_LEN	32
 #define DRM_DISPLAY_MODE_LEN	32
 #define DRM_PROP_NAME_LEN	32
+#define DRM_MODE_ATOMIC_FAILURE_STRING_LEN	64
 
 #define DRM_MODE_TYPE_BUILTIN	(1<<0) /* deprecated */
 #define DRM_MODE_TYPE_CLOCK_C	((1<<1) | DRM_MODE_TYPE_BUILTIN) /* deprecated */
@@ -1157,6 +1158,47 @@ struct drm_mode_destroy_dumb {
 		DRM_MODE_ATOMIC_NONBLOCK |\
 		DRM_MODE_ATOMIC_ALLOW_MODESET)
 
+#define DRM_MODE_ATOMIC_FAILURE_REASON \
+	FAILURE_REASON(DRM_MODE_ATOMIC_CAP_NOT_ENABLED, "DRM_ATOMIC capability not enabled") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_INVALID_FLAG, "invalid flag") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_PAGE_FLIP_ASYNC, "Legacy DRM_MODE_PAGE_FLIP_ASYNC not to be used in atomic ioctl") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_FLIP_EVENT_WITH_CHECKONLY, "requesting page-flip event with TEST_ONLY") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_CRTC_NEED_FULL_MODESET, "Need full modeset on this crtc") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_NEED_FULL_MODESET, "Need full modeset on all the connected crtc's") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_ASYNC_NOT_SUP_PLANE, "Async flip not supported on this plane") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_ASYNC_MODIFIER_NOT_SUPPORTED, "Modifier not supported on this plane with async flip") \
+	FAILURE_REASON(DRM_MODE_ATOMIC_ASYNC_PROP_CHANGED, "No property change allowed when async flip is enabled")
+
+#define FAILURE_REASON(flag, reason) flag,
+typedef enum {
+	DRM_MODE_ATOMIC_FAILURE_REASON
+} drm_mode_atomic_failure_flag;
+#undef FAILURE_REASON
+
+#define FAILURE_REASON(flag, reason) #reason,
+extern const char *drm_mode_atomic_failure_string[];
+#undef FAILURE_REASON
+
+/**
+ * drm_mode_atomic_err_code - struct to store the error code
+ *
+ * pointer to this struct will be stored in reserved variable of
+ * struct drm_mode_atomic to report the failure cause to the user.
+ *
+ * @failure_flags: error codes defined in drm_atomic_failure.failure_flag
+ * @failure_string_ptr: pointer to user readable error message drm_mode_failure.failure_string
+ * @failure_obj_ptr: pointer to the drm_object that caused error
+ * @reserved: reserved for future use
+ * @count_objs: count of drm_objects if multiple drm_objects caused error
+ */
+struct drm_mode_atomic_err_code {
+	__u64 failure_flags;
+	__u64 failure_objs_ptr;
+	__u64 reserved;
+	__u32 count_objs;
+	char failure_string[DRM_MODE_ATOMIC_FAILURE_STRING_LEN];
+};
+
 struct drm_mode_atomic {
 	__u32 flags;
 	__u32 count_objs;

-- 
2.25.1