[PATCH v11 1/7] drm: Define user readable error codes for atomic ioctl

[Arun R Murthy <arun.r.murthy@intel.com>]

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 retry. 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, thereby creation of new
uapi/interface for returning the error code is not required.
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 as a string can also be added
on need basis by the variable failure_string in the same struct
drm_mode_atomic_err_code.

v3: Remove fixed error (Jani/Xaver)
v5: Fix kernel-doc (Jani)
v7: Rephrase the kernel doc description (Suraj)
v8: Removed the below enum and suggest to use INVALID_API_USAGE (Xaver)
	DRM_MODE_ATOMIC_ASYNC_NOT_SUPP_PLANE
	DRM_MODE_ATOMIC_ASYNC_MODIFIER_NOT_SUPP
v10: Added more error codes for the enum
v11: Add default/unspecified error code

Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
---
 include/uapi/drm/drm_mode.h | 56 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index a4bdc4bd11bc142e9d3b172397e18a1909a21488..8bf5fd8533912dc7a188aad19cc3741dd2099592 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -48,6 +48,7 @@ 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	128
 
 #define DRM_MODE_TYPE_BUILTIN	(1<<0) /* deprecated */
 #define DRM_MODE_TYPE_CLOCK_C	((1<<1) | DRM_MODE_TYPE_BUILTIN) /* deprecated */
@@ -1346,6 +1347,61 @@ struct drm_mode_destroy_dumb {
 		DRM_MODE_ATOMIC_NONBLOCK |\
 		DRM_MODE_ATOMIC_ALLOW_MODESET)
 
+/**
+ * enum drm_mode_atomic_failure_codes -  error codes for failures in atomic_ioctl
+ * @DRM_MODE_ATOMIC_UNSPECIFIED_ERROR: this is the default/unspecified error.
+ * @DRM_MODE_ATOMIC_INVALID_API_USAGE: invallid API usage(DRM_ATOMIC not
+ *				       enabled, invalid falg, page_flip event
+ *				       with test-only, etc)
+ * @DRM_MODE_ATOMIC_NEED_FULL_MODESET: Need full modeset on all connected crtc's
+ * @DRM_MODE_ATOMIC_ASYNC_PROP_CHANGED: Property changed in async flip
+ * @DRM_MODE_ATOMIC_SCANOUT_BW: For a given resolution, refresh rate and the
+ *                              color depth cannot be accomodated. Resolution
+ *                              is to lower the refresh rate or color depth.
+ * @DRM_MODE_ATOMIC_CONNECTOR_BW: Refers to the limitation on the link rate on
+ *                                a given connector.
+ * @DRM_MODE_ATOMIC_PIPE_BW: Limitation on the pipe, either pipe not available
+ *                           or the pipe scaling factor limitation.
+ * @DRM_MODE_ATOMIC_MEMORY_DOMAIN: Any other memory/bandwidth related limitation
+ *                                 other then the ones specified above.
+ * @DRM_MODE_ATOMIC_SPEC_VIOLOATION: Limitation of a particular feature on that
+ *                                   hardware. To get to know the feature, the
+ *                                   property/object causing this is being sent
+ *                                   back to user @failure_objs_ptr in the
+ *                                   struct drm_mode_atomic_err_code
+ */
+enum drm_mode_atomic_failure_codes {
+	DRM_MODE_ATOMIC_UNSPECIFIED_ERROR,
+	DRM_MODE_ATOMIC_INVALID_API_USAGE,
+	DRM_MODE_ATOMIC_NEED_FULL_MODESET,
+	DRM_MODE_ATOMIC_ASYNC_PROP_CHANGED,
+	DRM_MODE_ATOMIC_SCANOUT_BW,
+	DRM_MODE_ATTOMIC_CONNECTOR_BW,
+	DRM_MODE_ATTOMIC_PIPE_BW,
+	DRM_MODE_ATOMIC_MEMORY_DOMAIN,
+	DRM_MODE_ATOMIC_SPEC_VIOLOATION,
+};
+
+/**
+ * struct 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_code: error codes defined in enum drm_moide_atomic_failure_code
+ * @failure_objs_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
+ * @failure_string: user readable error message string
+ */
+struct drm_mode_atomic_err_code {
+	__u64 failure_code;
+	__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