On Fri, 2026-07-10 at 20:52 +0200, Christian König wrote:
> Restructure the drm_exec object to work with dma_resv references
> instead
> of GEM object references.
>
> Add the new function dma_exec_lock_resv() to lock individual dma_resv
> objects and so allow higher level implementations to handle
> contention
> purely on dma_resv objects.
>
> WIP! Don't commit like that!
>
> Signed-off-by: Christian König <[email protected]>
Here, IMO we should move a dma-resv based implementation to dma-buf to
facilitate passing it also through dma_buf_map(),
And if wanting to avoid rewriting all users of drm_exec, Make drm_exec
a thin wrapper on top.
Thanks,
Thomas
> ---
> drivers/gpu/drm/drm_exec.c | 75 ++++++++++++++++++++++--------------
> --
> drivers/gpu/drm/drm_gem.c | 2 +
> include/drm/drm_exec.h | 9 +++--
> 3 files changed, 50 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_exec.c b/drivers/gpu/drm/drm_exec.c
> index fa923852fae45..382bf7bcd5ff3 100644
> --- a/drivers/gpu/drm/drm_exec.c
> +++ b/drivers/gpu/drm/drm_exec.c
> @@ -58,8 +58,11 @@ static void drm_exec_unlock_all(struct drm_exec
> *exec)
> drm_gem_object_put(obj);
> }
>
> - drm_gem_object_put(exec->prelocked);
> - exec->prelocked = NULL;
> + if (exec->prelocked) {
> + dma_resv_unlock(exec->prelocked);
> + dma_resv_put(exec->prelocked);
> + exec->prelocked = NULL;
> + }
> }
>
> /**
> @@ -101,7 +104,7 @@ void drm_exec_fini(struct drm_exec *exec)
> drm_exec_unlock_all(exec);
> kvfree(exec->objects);
> if (exec->contended != DRM_EXEC_DUMMY) {
> - drm_gem_object_put(exec->contended);
> + dma_resv_put(exec->contended);
> ww_acquire_fini(&exec->ticket);
> }
> }
> @@ -158,50 +161,41 @@ static int drm_exec_obj_locked(struct drm_exec
> *exec,
> /* Make sure the contended object is locked first */
> static int drm_exec_lock_contended(struct drm_exec *exec)
> {
> - struct drm_gem_object *obj = exec->contended;
> + struct dma_resv *resv = exec->contended;
> int ret;
>
> - if (likely(!obj))
> + if (likely(!resv))
> return 0;
>
> /* Always cleanup the contention so that error handling can
> kick in */
> exec->contended = NULL;
> if (exec->flags & DRM_EXEC_INTERRUPTIBLE_WAIT) {
> - ret = dma_resv_lock_slow_interruptible(obj->resv,
> - &exec-
> >ticket);
> + ret = dma_resv_lock_slow_interruptible(resv, &exec-
> >ticket);
> if (unlikely(ret))
> goto error_dropref;
> } else {
> - dma_resv_lock_slow(obj->resv, &exec->ticket);
> + dma_resv_lock_slow(resv, &exec->ticket);
> }
>
> - ret = drm_exec_obj_locked(exec, obj);
> - if (unlikely(ret))
> - goto error_unlock;
> -
> - exec->prelocked = obj;
> + exec->prelocked = resv;
> return 0;
>
> -error_unlock:
> - dma_resv_unlock(obj->resv);
> -
> error_dropref:
> - drm_gem_object_put(obj);
> + dma_resv_put(resv);
> return ret;
> }
>
> /**
> - * drm_exec_lock_obj - lock a GEM object for use
> + * drm_exec_lock_resv - lock a dma_resv object
> * @exec: the drm_exec object with the state
> - * @obj: the GEM object to lock
> + * @resv: the dma_resv object to lock
> *
> - * Lock a GEM object for use and grab a reference to it.
> + * Lock a dma_resv object for use or grab a reference to it on
> contention.
> *
> * Returns: -EDEADLK if a contention is detected, -EALREADY when
> object is
> - * already locked (can be suppressed by setting the
> DRM_EXEC_IGNORE_DUPLICATES
> - * flag), -ENOMEM when memory allocation failed and zero for
> success.
> + * already locked, -ENOMEM when memory allocation failed and zero
> for success.
> */
> -int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object
> *obj)
> +int drm_exec_lock_resv(struct drm_exec *exec, struct dma_resv *resv)
> {
> int ret;
>
> @@ -209,22 +203,39 @@ int drm_exec_lock_obj(struct drm_exec *exec,
> struct drm_gem_object *obj)
> if (unlikely(ret))
> return ret;
>
> - if (exec->prelocked == obj) {
> - drm_gem_object_put(exec->prelocked);
> + if (exec->prelocked == resv) {
> + dma_resv_put(exec->prelocked);
> exec->prelocked = NULL;
> return 0;
> }
>
> if (exec->flags & DRM_EXEC_INTERRUPTIBLE_WAIT)
> - ret = dma_resv_lock_interruptible(obj->resv, &exec-
> >ticket);
> + ret = dma_resv_lock_interruptible(resv, &exec-
> >ticket);
> else
> - ret = dma_resv_lock(obj->resv, &exec->ticket);
> + ret = dma_resv_lock(resv, &exec->ticket);
>
> - if (unlikely(ret == -EDEADLK)) {
> - drm_gem_object_get(obj);
> - exec->contended = obj;
> - return -EDEADLK;
> - }
> + if (unlikely(ret == -EDEADLK))
> + exec->contended = dma_resv_get(resv);
> + return ret;
> +}
> +EXPORT_SYMBOL(drm_exec_lock_resv);
> +
> +/**
> + * drm_exec_lock_obj - lock a GEM object for use
> + * @exec: the drm_exec object with the state
> + * @obj: the GEM object to lock
> + *
> + * Lock a GEM object for use and grab a reference to it.
> + *
> + * Returns: -EDEADLK if a contention is detected, -EALREADY when
> object is
> + * already locked (can be suppressed by setting the
> DRM_EXEC_IGNORE_DUPLICATES
> + * flag), -ENOMEM when memory allocation failed and zero for
> success.
> + */
> +int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object
> *obj)
> +{
> + int ret;
> +
> + ret = drm_exec_lock_resv(exec, obj->resv);
>
> if (unlikely(ret == -EALREADY) &&
> exec->flags & DRM_EXEC_IGNORE_DUPLICATES)
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index bbcbd25f014f0..f5cf9ad596a67 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -229,6 +229,8 @@ void drm_gem_private_object_init(struct
> drm_device *dev,
> obj->size = size;
> mutex_init(&obj->gpuva.lock);
> dma_resv_init(&obj->_resv);
> +
> + /* TODO: This needs to go away for drm_exec to work
> correctly!!! */
> if (!obj->resv)
> obj->resv = dma_resv_get(&obj->_resv);
>
> diff --git a/include/drm/drm_exec.h b/include/drm/drm_exec.h
> index 8725ba92ff916..9daedb676d7b1 100644
> --- a/include/drm/drm_exec.h
> +++ b/include/drm/drm_exec.h
> @@ -47,14 +47,14 @@ struct drm_exec {
> struct drm_gem_object **objects;
>
> /**
> - * @contended: contended GEM object we backed off for
> + * @contended: contended dma_resv object we backed off for
> */
> - struct drm_gem_object *contended;
> + struct dma_resv *contended;
>
> /**
> - * @prelocked: already locked GEM object due to contention
> + * @prelocked: already locked dma_resv object due to
> contention
> */
> - struct drm_gem_object *prelocked;
> + struct dma_resv *prelocked;
> };
>
> /**
> @@ -175,6 +175,7 @@ static inline struct ww_acquire_ctx
> *drm_exec_ticket(struct drm_exec *exec)
> void drm_exec_init(struct drm_exec *exec, u32 flags, unsigned nr);
> void drm_exec_fini(struct drm_exec *exec);
> bool drm_exec_cleanup(struct drm_exec *exec);
> +int drm_exec_lock_resv(struct drm_exec *exec, struct dma_resv
> *resv);
> int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object
> *obj);
> void drm_exec_unlock_obj(struct drm_exec *exec, struct
> drm_gem_object *obj);
> int drm_exec_prepare_obj(struct drm_exec *exec, struct
> drm_gem_object *obj,
