On Tue, 02 Sep 2025, Arun R Murthy <[email protected]> wrote:
> 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 <[email protected]>
Please run 'scripts/kernel-doc -Wall -none path/to/file' on all changes,
and make sure you're not adding new errors. There are plenty, and I'm
not going to iterate to you separately what the tool can tell you.
> ---
> include/uapi/drm/drm_mode.h | 41 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 41 insertions(+)
>
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index
> a122bea2559387576150236e3a88f99c24ad3138..6c4929e591b30b7a5eac472dadeeb3c9400e36df
> 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
64 is enough for everyone?
>
> #define DRM_MODE_TYPE_BUILTIN (1<<0) /* deprecated */
> #define DRM_MODE_TYPE_CLOCK_C ((1<<1) | DRM_MODE_TYPE_BUILTIN) /*
> deprecated */
> @@ -1157,6 +1158,46 @@ struct drm_mode_destroy_dumb {
> DRM_MODE_ATOMIC_NONBLOCK |\
> DRM_MODE_ATOMIC_ALLOW_MODESET)
>
> +/**
> + * enum drm_mode_atomic_err_code - error codes for failures in atomic_ioctl
> + * @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_CRTC_NEED_FULL_MODESET: Need full modeset on this crtc
> + * @DRM_MODE_ATOMIC_NEED_FULL_MODESET: Need full modeset on all connected
> crtc's
> + * @DRM_MODE_ATOMIC_ASYN_NOTSUPP_PLANE: Aync flip not supported on this plane
> + * DRM_MODE_ATOMIC_ASYNC_MODIFIER_NOT_SUPP: Modifier not supported by async
> flip
> + * @DRM_MODE_ATOMIC_ASYNC_PROP_CHANGED: Property changed in async flip
> + */
> +enum drm_mode_atomic_failure_codes {
> + DRM_MODE_ATOMIC_INVALID_API_USAGE,
> + DRM_MODE_ATOMIC_CRTC_NEED_FULL_MODESET,
> + DRM_MODE_ATOMIC_NEED_FULL_MODESET,
> + DRM_MODE_ATOMIC_ASYNC_NOT_SUPP_PLANE,
> + DRM_MODE_ATOMIC_ASYNC_MODIFIER_NOT_SUPP,
> + DRM_MODE_ATOMIC_ASYNC_PROP_CHANGED,
> +};
> +
> +/**
> + * 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_string_ptr: pointer to user readable error message 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_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;
--
Jani Nikula, Intel
