[PATCH] drm/atomic: skip ww_acquire_done() for legacy paths

[Daniel Vetter]

On Tue, Aug 18, 2015 at 11:54 AM, Rob Clark <robdclark at gmail.com> wrote:
> The addition of ww_acquire_done() call to mark the point where all locks
> should already be held, added in:
>
>   commit 992cbf19b32900efa17850b9fa0031fd623edd4d
>   Author:     Daniel Vetter <daniel.vetter at ffwll.ch>
>   AuthorDate: Thu Aug 6 15:06:40 2015 +0200
>
>       drm/atomic: Call ww_acquire_done after check phase is complete
>
> missed the case that legacy paths (which are already called between
> drm_modeset_lock_all()/unlock_all()) re-use the single acquire ctx, even
> if there are multiple atomic updates.  For example, restore_fbdev_mode()
> clearing rotation properties individually on each plane.
>
> Inki already sent a patch which completely removed the ww_acquire_done()
> call, but I think this is less ideal (since it is a nice debugging
> feature of ww_mutex to confirm that everyone is following the rules).
> So instead, just skip the call only in the special legacy-path case.
>
> Reported-by: Inki Dae <inki.dae at samsung.com>
> Tested-by: Bjorn Andersson <bjorn.andersson at sonymobile.com>
> Signed-off-by: Rob Clark <robdclark at gmail.com>

Should we instead just do it in the atomic ioclt path? Your patch here
is missing the legacy crtc-update case (where the acquire_ctx is
stored in the drm_crtc). Also this won't work once we have a
drm_modeset_lock_all_ctx.
-Daniel

> ---
>  drivers/gpu/drm/drm_atomic.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 1066e4b..b90068c 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1230,8 +1230,15 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
>                 }
>         }
>
> -       if (ret == 0)
> -               ww_acquire_done(&state->acquire_ctx->ww_ctx);
> +       if (ret == 0) {
> +               /* in legacy paths, there can be multiple atomic updates,
> +                * such as drm_mode_plane_set_obj_prop(), which happen
> +                * under a single drm_modeset_lock_all().  In the legacy
> +                * paths, skip marking acquire-done lest we anger ww-mutex:
> +                */
> +               if (state->acquire_ctx != dev->mode_config.acquire_ctx)
> +                       ww_acquire_done(&state->acquire_ctx->ww_ctx);
> +       }
>
>         return ret;
>  }
> --
> 2.4.3
>



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch