Re: [PATCH 4/6] drm/panthor: Use guards for resv locking

[Chia-I Wu <olvaffe@gmail.com>]

On Wed, May 13, 2026 at 10:09 AM Boris Brezillon
<boris.brezillon@collabora.com> wrote:
>
> Now that we have guards for resv locks, we can use them to simplify the
> core. The only manual lock/unlock remaining are the ones in
> panthor_gem_try_evict_no_resv_wait(), because the lock/unlock are
> in different for_each() loop scopes.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 77 ++++++++++++-----------------------
>  drivers/gpu/drm/panthor/panthor_mmu.c | 16 ++++----
>  2 files changed, 32 insertions(+), 61 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index a6fddc380e7d..94facdc8cfe1 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -339,13 +339,9 @@ panthor_gem_dev_map_get_sgt_locked(struct panthor_gem_object *bo)
>  struct sg_table *
>  panthor_gem_get_dev_sgt(struct panthor_gem_object *bo)
>  {
> -       struct sg_table *sgt;
> +       guard(dma_resv)(bo->base.resv);
>
> -       dma_resv_lock(bo->base.resv, NULL);
> -       sgt = panthor_gem_dev_map_get_sgt_locked(bo);
> -       dma_resv_unlock(bo->base.resv);
> -
> -       return sgt;
> +       return panthor_gem_dev_map_get_sgt_locked(bo);
>  }
>
>  static void
> @@ -497,7 +493,7 @@ panthor_gem_prime_begin_cpu_access(struct dma_buf *dma_buf,
>         struct panthor_gem_object *bo = to_panthor_bo(obj);
>         struct dma_buf_attachment *attach;
>
> -       dma_resv_lock(obj->resv, NULL);
> +       guard(dma_resv)(obj->resv);
>         if (bo->dmap.sgt)
>                 dma_sync_sgtable_for_cpu(drm_dev_dma_dev(dev), bo->dmap.sgt, dir);
>
> @@ -510,7 +506,6 @@ panthor_gem_prime_begin_cpu_access(struct dma_buf *dma_buf,
>                 if (sgt)
>                         dma_sync_sgtable_for_cpu(attach->dev, sgt, dir);
>         }
> -       dma_resv_unlock(obj->resv);
>
>         return 0;
>  }
> @@ -524,7 +519,7 @@ panthor_gem_prime_end_cpu_access(struct dma_buf *dma_buf,
>         struct panthor_gem_object *bo = to_panthor_bo(obj);
>         struct dma_buf_attachment *attach;
>
> -       dma_resv_lock(obj->resv, NULL);
> +       guard(dma_resv)(obj->resv);
>         list_for_each_entry(attach, &dma_buf->attachments, node) {
>                 struct sg_table *sgt = attach->priv;
>
> @@ -538,7 +533,6 @@ panthor_gem_prime_end_cpu_access(struct dma_buf *dma_buf,
>         if (bo->dmap.sgt)
>                 dma_sync_sgtable_for_device(drm_dev_dma_dev(dev), bo->dmap.sgt, dir);
>
> -       dma_resv_unlock(obj->resv);
>         return 0;
>  }
>
> @@ -625,19 +619,15 @@ static void panthor_gem_unpin_locked(struct drm_gem_object *obj)
>
>  int panthor_gem_pin(struct panthor_gem_object *bo)
>  {
> -       int ret = 0;
> -
>         if (drm_gem_is_imported(&bo->base))
>                 return 0;
>
>         if (refcount_inc_not_zero(&bo->backing.pin_count))
>                 return 0;
>
> -       dma_resv_lock(bo->base.resv, NULL);
> -       ret = panthor_gem_backing_pin_locked(bo);
> -       dma_resv_unlock(bo->base.resv);
> +       guard(dma_resv)(bo->base.resv);
>
> -       return ret;
> +       return panthor_gem_backing_pin_locked(bo);
>  }
>
>  void panthor_gem_unpin(struct panthor_gem_object *bo)
> @@ -648,9 +638,8 @@ void panthor_gem_unpin(struct panthor_gem_object *bo)
>         if (refcount_dec_not_one(&bo->backing.pin_count))
>                 return;
>
> -       dma_resv_lock(bo->base.resv, NULL);
> +       guard(dma_resv)(bo->base.resv);
>         panthor_gem_backing_unpin_locked(bo);
> -       dma_resv_unlock(bo->base.resv);
>  }
>
>  int panthor_gem_swapin_locked(struct panthor_gem_object *bo)
> @@ -759,13 +748,12 @@ static int panthor_gem_mmap(struct drm_gem_object *obj, struct vm_area_struct *v
>                 return -EINVAL;
>
>         if (!refcount_inc_not_zero(&bo->cmap.mmap_count)) {
> -               dma_resv_lock(obj->resv, NULL);
> +               guard(dma_resv)(obj->resv);
>                 if (!refcount_inc_not_zero(&bo->cmap.mmap_count)) {
>                         refcount_set(&bo->cmap.mmap_count, 1);
>                         guard(mutex)(&bo->base.gpuva.lock);
>                         panthor_gem_update_reclaim_state_locked(bo, NULL);
>                 }
> -               dma_resv_unlock(obj->resv);
>         }
>
>         vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
> @@ -814,18 +802,12 @@ static vm_fault_t nonblocking_page_setup(struct vm_fault *vmf,
>  {
>         struct vm_area_struct *vma = vmf->vma;
>         struct panthor_gem_object *bo = to_panthor_bo(vma->vm_private_data);
> -       vm_fault_t ret;
>
> -       if (!dma_resv_trylock(bo->base.resv))
> +       ACQUIRE(dma_resv_try, resv_guard)(bo->base.resv);
> +       if (ACQUIRE_ERR(dma_resv_try, &resv_guard) || !bo->backing.pages)
>                 return VM_FAULT_RETRY;
>
> -       if (bo->backing.pages)
> -               ret = insert_page(vmf, order, bo->backing.pages[page_offset]);
> -       else
> -               ret = VM_FAULT_RETRY;
> -
> -       dma_resv_unlock(bo->base.resv);
> -       return ret;
> +       return insert_page(vmf, order, bo->backing.pages[page_offset]);
>  }
>
>  static vm_fault_t blocking_page_setup(struct vm_fault *vmf, unsigned int order,
> @@ -835,8 +817,8 @@ static vm_fault_t blocking_page_setup(struct vm_fault *vmf, unsigned int order,
>         vm_fault_t ret;
>         int err;
>
> -       err = dma_resv_lock_interruptible(bo->base.resv, NULL);
> -       if (err)
> +       ACQUIRE(dma_resv_intr, resv_guard)(bo->base.resv);
> +       if (ACQUIRE_ERR(dma_resv_intr, &resv_guard))
>                 return mmap_lock_held ? VM_FAULT_NOPAGE : VM_FAULT_RETRY;
>
>         err = panthor_gem_backing_get_pages_locked(bo);
> @@ -857,8 +839,6 @@ static vm_fault_t blocking_page_setup(struct vm_fault *vmf, unsigned int order,
>                         ret = VM_FAULT_RETRY;
>         }
>
> -       dma_resv_unlock(bo->base.resv);
> -
>         return ret;
>  }
>
> @@ -932,12 +912,12 @@ static void panthor_gem_vm_close(struct vm_area_struct *vma)
>         if (refcount_dec_not_one(&bo->cmap.mmap_count))
>                 goto out;
>
> -       dma_resv_lock(bo->base.resv, NULL);
> -       if (refcount_dec_and_test(&bo->cmap.mmap_count)) {
> -               guard(mutex)(&bo->base.gpuva.lock);
> -               panthor_gem_update_reclaim_state_locked(bo, NULL);
> +       scoped_guard(dma_resv, bo->base.resv) {
> +               if (refcount_dec_and_test(&bo->cmap.mmap_count)) {
> +                       guard(mutex)(&bo->base.gpuva.lock);
> +                       panthor_gem_update_reclaim_state_locked(bo, NULL);
> +               }
>         }
> -       dma_resv_unlock(bo->base.resv);
>
>  out:
>         drm_gem_object_put(&bo->base);
> @@ -1161,21 +1141,18 @@ panthor_gem_sync(struct drm_gem_object *obj, u32 type,
>         if (size == 0)
>                 return 0;
>
> -       ret = dma_resv_lock_interruptible(bo->base.resv, NULL);
> +       ACQUIRE(dma_resv_intr, resv_guard)(bo->base.resv);
> +       ret = ACQUIRE_ERR(dma_resv_intr, &resv_guard);
>         if (ret)
>                 return ret;
>
>         /* If there's no pages, there's no point pulling those back, bail out early. */
> -       if (!bo->backing.pages) {
> -               ret = 0;
> -               goto out_unlock;
> -       }
> +       if (!bo->backing.pages)
> +               return 0;
>
>         sgt = panthor_gem_dev_map_get_sgt_locked(bo);
> -       if (IS_ERR(sgt)) {
> -               ret = PTR_ERR(sgt);
> -               goto out_unlock;
> -       }
> +       if (IS_ERR(sgt))
> +               return PTR_ERR(sgt);
>
>         for_each_sgtable_dma_sg(sgt, sgl, count) {
>                 if (size == 0)
> @@ -1219,11 +1196,7 @@ panthor_gem_sync(struct drm_gem_object *obj, u32 type,
>                         dma_sync_single_for_cpu(dma_dev, paddr, len, DMA_FROM_DEVICE);
>         }
>
> -       ret = 0;
> -
> -out_unlock:
> -       dma_resv_unlock(bo->base.resv);
> -       return ret;
> +       return 0;
>  }
>
>  /**
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 157eef286cb9..ab9a77e6a145 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1118,10 +1118,10 @@ static void panthor_vm_bo_free(struct drm_gpuvm_bo *vm_bo)
>         /* We couldn't call this when we unlinked, because the resv lock can't
>          * be taken in the dma signalling path, so call it now.
>          */
> -       dma_resv_lock(bo->base.resv, NULL);
> -       scoped_guard(mutex, &bo->base.gpuva.lock)
> +       scoped_guard(dma_resv, bo->base.resv) {
> +               guard(mutex)(&bo->base.gpuva.lock);
>                 panthor_gem_update_reclaim_state_locked(bo, NULL);
> -       dma_resv_unlock(bo->base.resv);
> +       }
>
>         kfree(vm_bo);
>  }
> @@ -1342,16 +1342,14 @@ static int panthor_vm_prepare_map_op_ctx(struct panthor_vm_op_ctx *op_ctx,
>
>         /* Insert BO into the extobj list last, when we know nothing can fail. */
>         if (bo->base.resv != panthor_vm_resv(vm)) {
> -               dma_resv_lock(panthor_vm_resv(vm), NULL);
> +               guard(dma_resv)(panthor_vm_resv(vm));
>                 drm_gpuvm_bo_extobj_add(op_ctx->map.vm_bo);
> -               dma_resv_unlock(panthor_vm_resv(vm));
>         }
>
>         /* And finally update the BO state. */
> -       dma_resv_lock(bo->base.resv, NULL);
> -       scoped_guard(mutex, &bo->base.gpuva.lock)
> -               panthor_gem_update_reclaim_state_locked(bo, NULL);
> -       dma_resv_unlock(bo->base.resv);
> +       guard(dma_resv)(bo->base.resv);
> +       guard(mutex)(&bo->base.gpuva.lock);
> +       panthor_gem_update_reclaim_state_locked(bo, NULL);
>
>         return 0;
>
>
> --
> 2.54.0
>