[Freedreno] [RFC] drm: return int error code from mode_fixup

[Daniel Vetter]

On Tue, Jul 13, 2021 at 7:14 PM Grace An <gracan at codeaurora.org> wrote:
> When CONFIG_PROVE_LOCKING is defined, the kernel randomly injects
> -EDEADLK errors for all the ww_mutex. This results in
> drm_atomic_get_private_obj_state randomly returning -EDEADLK.
> However, the mode_fixup functions do not propagate these error
> codes and return false, causing the atomic commit to fail with
> -EINVAL instead of retrying.
>
> Change encoder, crtc, and bridge mode_fixup functions to return
> an int instead of a boolean to indicate success or failure. If
> any of these functions fail, the mode_fixup function now returns
> the provided integer error code instead of -EINVAL.
>
> This change needs modifications across drivers, but before submitting
> the entire change, we want to get feedback on this RFC.
>
> Signed-off-by: Grace An <gracan at codeaurora.org>

Why don't you just use the various atomic_check hooks we have for
this? There you get passed the state and everything, have a full int
return value, and things actually work.

->mode_fixup is for compatibility with legacy crtc modeset helpers
from the pre-atomic times. If the kerneldoc isn't clear yet, please do
a patch to fix that up so that @mode_fixup points at the relevant
@atomic_check as the recommended function.
-Daniel

> ---
>  drivers/gpu/drm/drm_atomic_helper.c      | 8 ++++----
>  drivers/gpu/drm/drm_bridge.c             | 4 ++--
>  include/drm/drm_bridge.h                 | 2 +-
>  include/drm/drm_modeset_helper_vtables.h | 4 ++--
>  4 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index f2b3e28..d75f09a 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -457,10 +457,10 @@ mode_fixup(struct drm_atomic_state *state)
>                 } else if (funcs && funcs->mode_fixup) {
>                         ret = funcs->mode_fixup(encoder, &new_crtc_state->mode,
>                                                 &new_crtc_state->adjusted_mode);
> -                       if (!ret) {
> +                       if (ret) {
>                                 DRM_DEBUG_ATOMIC("[ENCODER:%d:%s] fixup failed\n",
>                                                  encoder->base.id, encoder->name);
> -                               return -EINVAL;
> +                               return ret;
>                         }
>                 }
>         }
> @@ -481,10 +481,10 @@ mode_fixup(struct drm_atomic_state *state)
>
>                 ret = funcs->mode_fixup(crtc, &new_crtc_state->mode,
>                                         &new_crtc_state->adjusted_mode);
> -               if (!ret) {
> +               if (ret) {
>                         DRM_DEBUG_ATOMIC("[CRTC:%d:%s] fixup failed\n",
>                                          crtc->base.id, crtc->name);
> -                       return -EINVAL;
> +                       return ret;
>                 }
>         }
>
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 64f0eff..3ad16b5 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -736,9 +736,9 @@ static int drm_atomic_bridge_check(struct drm_bridge *bridge,
>                 if (ret)
>                         return ret;
>         } else if (bridge->funcs->mode_fixup) {
> -               if (!bridge->funcs->mode_fixup(bridge, &crtc_state->mode,
> +               if (bridge->funcs->mode_fixup(bridge, &crtc_state->mode,
>                                                &crtc_state->adjusted_mode))
> -                       return -EINVAL;
> +                       return ret;
>         }
>
>         return 0;
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 2195daa..5d02dfc 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -153,7 +153,7 @@ struct drm_bridge_funcs {
>          * True if an acceptable configuration is possible, false if the modeset
>          * operation should be rejected.
>          */
> -       bool (*mode_fixup)(struct drm_bridge *bridge,
> +       int (*mode_fixup)(struct drm_bridge *bridge,
>                            const struct drm_display_mode *mode,
>                            struct drm_display_mode *adjusted_mode);
>         /**
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index f3a4b47..e305c97 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -184,7 +184,7 @@ struct drm_crtc_helper_funcs {
>          * True if an acceptable configuration is possible, false if the modeset
>          * operation should be rejected.
>          */
> -       bool (*mode_fixup)(struct drm_crtc *crtc,
> +       int (*mode_fixup)(struct drm_crtc *crtc,
>                            const struct drm_display_mode *mode,
>                            struct drm_display_mode *adjusted_mode);
>
> @@ -599,7 +599,7 @@ struct drm_encoder_helper_funcs {
>          * True if an acceptable configuration is possible, false if the modeset
>          * operation should be rejected.
>          */
> -       bool (*mode_fixup)(struct drm_encoder *encoder,
> +       int (*mode_fixup)(struct drm_encoder *encoder,
>                            const struct drm_display_mode *mode,
>                            struct drm_display_mode *adjusted_mode);
>
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch