On 15/10/2025 14:00, Boris Brezillon wrote: > From: Faith Ekstrand <[email protected]> > > This enables syncing mapped GEM objects between the CPU and GPU via calls > to dma_sync_*(). It's a bit annoying as it requires walking the sg_table > so it's best if every driver doesn't hand-roll it. > > When we're dealing with a dma-buf, the synchronization requests are > forwarded to the exporter through dma_buf_{begin,end}_cpu_access(). > > We provide a drm_gem_shmem_object_sync() for drivers that wants to > have this default implementation as their drm_gem_object_funcs::sync, > but we don't set drm_gem_shmem_funcs::sync to > drm_gem_shmem_object_sync() to avoid changing the behavior of drivers > currently relying on the default gem_shmem vtable. > > v2: > - s/drm_gem_shmem_sync_mmap/drm_gem_shmem_sync/ > - Change the prototype to match drm_gem_object_funcs::sync() > - Add a wrapper for drm_gem_object_funcs::sync() > > v3: > - No changes > > Signed-off-by: Faith Ekstrand <[email protected]> > Signed-off-by: Boris Brezillon <[email protected]>
Reviewed-by: Steven Price <[email protected]> > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 89 ++++++++++++++++++++++++++ > include/drm/drm_gem_shmem_helper.h | 11 ++++ > 2 files changed, 100 insertions(+) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c > b/drivers/gpu/drm/drm_gem_shmem_helper.c > index dc94a27710e5..4094bd243cc8 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -690,6 +690,95 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object > *shmem, struct vm_area_struct > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_mmap); > > +/** > + * drm_gem_shmem_sync - Sync CPU-mapped data to/from the device > + * @shmem: shmem GEM object > + * @offset: Offset into the GEM object > + * @size: Size of the area to sync > + * @access: Flags describing the access to sync for > + * > + * Returns: > + * 0 on success or a negative error code on failure. > + */ > +int drm_gem_shmem_sync(struct drm_gem_shmem_object *shmem, size_t offset, > + size_t size, enum drm_gem_object_access_flags access) > +{ > + bool for_dev = (access & DRM_GEM_OBJECT_ACCESSOR_MASK) == > DRM_GEM_OBJECT_DEV_ACCESS; > + u32 access_type = access & DRM_GEM_OBJECT_ACCESS_TYPE_MASK; > + struct drm_device *dev = shmem->base.dev; > + enum dma_data_direction dir; > + struct sg_table *sgt; > + struct scatterlist *sgl; > + unsigned int count; > + > + if (access_type == DRM_GEM_OBJECT_RW_ACCESS) > + dir = DMA_BIDIRECTIONAL; > + else if (access_type == DRM_GEM_OBJECT_READ_ACCESS) > + dir = for_dev ? DMA_TO_DEVICE : DMA_FROM_DEVICE; > + else if (access_type == DRM_GEM_OBJECT_WRITE_ACCESS) > + dir = for_dev ? DMA_FROM_DEVICE : DMA_TO_DEVICE; > + else > + return 0; > + > + /* Don't bother if it's WC-mapped */ > + if (shmem->map_wc) > + return 0; > + > + if (size == 0) > + return 0; > + > + if (offset + size < offset || offset + size > shmem->base.size) > + return -EINVAL; > + > + if (drm_gem_is_imported(&shmem->base)) { > + /* We can't do fine-grained syncs with dma_buf and there's no > + * easy way to guarantee that CPU caches/memory won't get > + * impacted by the buffer-wide synchronization, so let's fail > + * instead of pretending we can cope with that. > + */ > + if (offset != 0 || size != shmem->base.size) > + return -EINVAL; > + > + struct dma_buf *dma_buf = shmem->base.import_attach->dmabuf; > + > + if (for_dev) > + return dma_buf_end_cpu_access(dma_buf, dir); > + else > + return dma_buf_begin_cpu_access(dma_buf, dir); > + } > + > + sgt = drm_gem_shmem_get_pages_sgt(shmem); > + if (IS_ERR(sgt)) > + return PTR_ERR(sgt); > + > + for_each_sgtable_dma_sg(sgt, sgl, count) { > + if (size == 0) > + break; > + > + dma_addr_t paddr = sg_dma_address(sgl); > + size_t len = sg_dma_len(sgl); > + > + if (len <= offset) { > + offset -= len; > + continue; > + } > + > + paddr += offset; > + len -= offset; > + len = min_t(size_t, len, size); > + size -= len; > + offset = 0; > + > + if (for_dev) > + dma_sync_single_for_device(dev->dev, paddr, len, dir); > + else > + dma_sync_single_for_cpu(dev->dev, paddr, len, dir); > + } > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(drm_gem_shmem_sync); > + > /** > * drm_gem_shmem_print_info() - Print &drm_gem_shmem_object info for debugfs > * @shmem: shmem GEM object > diff --git a/include/drm/drm_gem_shmem_helper.h > b/include/drm/drm_gem_shmem_helper.h > index 589f7bfe7506..6363e4ac9163 100644 > --- a/include/drm/drm_gem_shmem_helper.h > +++ b/include/drm/drm_gem_shmem_helper.h > @@ -123,6 +123,8 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object > *shmem, > void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem, > struct iosys_map *map); > int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct > vm_area_struct *vma); > +int drm_gem_shmem_sync(struct drm_gem_shmem_object *shmem, size_t offset, > + size_t size, enum drm_gem_object_access_flags access); > > int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem); > void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem); > @@ -279,6 +281,15 @@ static inline int drm_gem_shmem_object_mmap(struct > drm_gem_object *obj, struct v > return drm_gem_shmem_mmap(shmem, vma); > } > > +static inline int > +drm_gem_shmem_object_sync(struct drm_gem_object *obj, size_t offset, > + size_t size, enum drm_gem_object_access_flags access) > +{ > + struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); > + > + return drm_gem_shmem_sync(shmem, offset, size, access); > +} > + > /* > * Driver ops > */
