On Wed, Sep 16, 2026 at 11:10:51PM +0200, Francesco Valla wrote: > Depending on the driver originating them, data buffers used for virtio > communication can either: > > - already be allocated from the coherent memory area that is > accessible by the remote processor; this is the case of rpmsg > and the rproc flavor of virtio-console; > - be allocated from generic kmem, and thus not accessible directly by > the remote processor. > > Exploiting the map operations, which are used by the virtio framework > when VIRTIO_F_ACCESS_PLATFORM is part of a vdev's feature flags, add > bounce buffering for the second case: when the map() callback is called > for a buffer, one or more pages of coherent memory are allocated and > data is copied to them, then they are exposed to the remote processor; > the data is then bounced back on unmap(). > > The first case is not impacted, since buffers already suitable for > remote transmission are passed through. > > With the bounce buffering in place, any kind of virtio device can be > supported through the remoteproc-virtio transport, at least from a > data exchange standpoint.
Is this _necessary_ for the imx93 platform you are implementing feature for? > > Signed-off-by: Francesco Valla <[email protected]> > --- > drivers/remoteproc/remoteproc_virtio.c | 182 > +++++++++++++++++++++++++++++++-- > include/linux/remoteproc.h | 14 +++ > 2 files changed, 190 insertions(+), 6 deletions(-) > > diff --git a/drivers/remoteproc/remoteproc_virtio.c > b/drivers/remoteproc/remoteproc_virtio.c > index cfd66d9d1c9e..d21b3b8044df 100644 > --- a/drivers/remoteproc/remoteproc_virtio.c > +++ b/drivers/remoteproc/remoteproc_virtio.c > @@ -241,7 +241,14 @@ static void rproc_virtio_reset(struct virtio_device > *vdev) > dev_dbg(&vdev->dev, "reset !\n"); > } > > -/* provide the vdev features as retrieved from the firmware */ > +/* Provide the vdev features as retrieved from the firmware, plus the > following > + * additional ones: > + * - VIRTIO_F_VERSION_1 that is required by some non-rpmsg virtio devices > + * - VIRTIO_F_ACCESS_PLATFORM to force usage of the map operations > + */ > +#define RPROC_VIRTIO_STATIC_FEATURES \ > + ((1ULL << VIRTIO_F_VERSION_1) | (1ULL << VIRTIO_F_ACCESS_PLATFORM)) > + > static u64 rproc_virtio_get_features(struct virtio_device *vdev) > { > struct rproc_vdev *rvdev = vdev_to_rvdev(vdev); > @@ -249,7 +256,7 @@ static u64 rproc_virtio_get_features(struct virtio_device > *vdev) > > rsc = (void *)rvdev->rproc->table_ptr + rvdev->rsc_offset; > > - return rsc->dfeatures | (1ULL << VIRTIO_F_VERSION_1); > + return rsc->dfeatures | RPROC_VIRTIO_STATIC_FEATURES; > } > > static void rproc_transport_features(struct virtio_device *vdev) > @@ -275,16 +282,16 @@ static int rproc_virtio_finalize_features(struct > virtio_device *vdev) > /* Give virtio_rproc a chance to accept features. */ > rproc_transport_features(vdev); > > - /* Make sure we don't have any features > 32 bits except > VIRTIO_F_VERSION_1 */ > + /* Make sure we don't have any features > 32 bits */ > if (WARN_ON_ONCE((u32)vdev->features != > - (vdev->features & ~(1ULL << VIRTIO_F_VERSION_1)))) > + (vdev->features & ~RPROC_VIRTIO_STATIC_FEATURES))) > return -1; > > /* > * Remember the finalized features of our vdev, and provide it > * to the remote processor once it is powered on. > */ > - rsc->gfeatures = vdev->features & ~(1ULL << VIRTIO_F_VERSION_1); > + rsc->gfeatures = vdev->features & ~RPROC_VIRTIO_STATIC_FEATURES; > > return 0; > } > @@ -337,6 +344,151 @@ static const struct virtio_config_ops > rproc_virtio_config_ops = { > .set = rproc_virtio_set, > }; > > +static inline unsigned int rproc_virtio_bounce_slot(struct device *dma_dev, > + dma_addr_t dma_handle) > +{ > + const dma_addr_t dma_base = dma_dev_coherent_base(dma_dev); > + > + return (dma_handle - dma_base) >> PAGE_SHIFT; > +} > + > +static dma_addr_t rproc_virtio_map_page(union virtio_map map, struct page > *page, > + unsigned long offset, size_t size, > + enum dma_data_direction dir, > + unsigned long attrs) > +{ > + struct device *dev = map.dma_dev; > + struct rproc_vdev *rvdev = dev_get_drvdata(dev); > + dma_addr_t dma_base = dma_dev_coherent_base(dev); > + size_t dma_size = dma_dev_coherent_size(dev); > + phys_addr_t paddr = page_to_phys(page) + offset; > + void *vaddr = page_to_virt(page) + offset; > + struct rproc_map_record *record; > + dma_addr_t map_handle; > + void *bounce; > + > + // No need to allocate a bounce buffer if the memory to map is already > + // part of the device's coherent pool. > + if (paddr >= dma_base && paddr < (dma_base + dma_size)) { > + // The allocation details will be recorded also in this case, > + // indicating that no bounce buffer was allocated. > + map_handle = (dma_addr_t)paddr; > + bounce = NULL; > + } else { > + // Allocate bounce buffer from device coherent memory > + bounce = dma_alloc_coherent(dev, size, &map_handle, GFP_KERNEL > | __GFP_ZERO); > + if (!bounce) > + return DMA_MAPPING_ERROR; > + > + // Copy data to bounce buffer > + memcpy(bounce, vaddr, size); > + } > + > + // Save bounce details > + record = &rvdev->map_records[rproc_virtio_bounce_slot(dev, map_handle)]; > + > + record->original = vaddr; > + record->size = size; > + record->bounce = bounce; > + > + return map_handle; > +} > + > +static void rproc_virtio_unmap_page(union virtio_map map, dma_addr_t > map_handle, > + size_t size, enum dma_data_direction dir, > + unsigned long attrs) > +{ > + struct device *dev = map.dma_dev; > + struct rproc_vdev *rvdev = dev_get_drvdata(dev); > + unsigned int slot = rproc_virtio_bounce_slot(dev, map_handle); > + struct rproc_map_record *record = &rvdev->map_records[slot]; > + > + WARN_ON(size != record->size); > + > + // If a bounce buffer was used, copy data back to original one > + if (record->bounce) { > + memcpy(record->original, record->bounce, record->size); > + > + dma_free_coherent(dev, record->size, record->bounce, > map_handle); > + } > + > + record->original = NULL; > + record->size = 0; > + record->bounce = NULL; > +} > + > +static void rproc_virtio_sync_single_for_cpu(union virtio_map map, > + dma_addr_t map_handle, > + size_t size, > + enum dma_data_direction dir) > +{ > + struct device *dev = map.dma_dev; > + > + dma_sync_single_range_for_cpu(dev, (map_handle & PAGE_MASK), > + offset_in_page(map_handle), size, dir); > +} > + > +static void rproc_virtio_sync_single_for_device(union virtio_map map, > + dma_addr_t map_handle, > + size_t size, > + enum dma_data_direction dir) > +{ > + struct device *dev = map.dma_dev; > + > + dma_sync_single_range_for_device(dev, (map_handle & PAGE_MASK), > + offset_in_page(map_handle), size, dir); > +} > + > +static void *rproc_virtio_alloc(union virtio_map map, size_t size, > + dma_addr_t *map_handle, gfp_t gfp) > +{ > + struct device *dev = map.dma_dev; > + > + return dma_alloc_coherent(dev, size, map_handle, gfp); > +} > + > +static void rproc_virtio_free(union virtio_map map, size_t size, void *vaddr, > + dma_addr_t map_handle, unsigned long attrs) > +{ > + struct device *dev = map.dma_dev; > + > + dma_free_coherent(dev, size, vaddr, map_handle); > +} > + > +static bool rproc_virtio_need_sync(union virtio_map map, dma_addr_t > map_handle) > +{ > + struct device *dev = map.dma_dev; > + > + return dma_need_sync(dev, map_handle); > +} > + > +static int rproc_virtio_mapping_error(union virtio_map map, dma_addr_t > map_handle) > +{ > + if (unlikely(map_handle == DMA_MAPPING_ERROR)) > + return -ENOMEM; > + > + return 0; > +} > + > +static inline size_t rproc_virtio_max_mapping_size(union virtio_map map) > +{ > + struct device *dev = map.dma_dev; > + > + return dma_dev_coherent_size(dev); > +} > + > +static const struct virtio_map_ops rproc_virtio_map_ops = { > + .map_page = rproc_virtio_map_page, > + .unmap_page = rproc_virtio_unmap_page, > + .sync_single_for_cpu = rproc_virtio_sync_single_for_cpu, > + .sync_single_for_device = rproc_virtio_sync_single_for_device, > + .alloc = rproc_virtio_alloc, > + .free = rproc_virtio_free, > + .need_sync = rproc_virtio_need_sync, > + .mapping_error = rproc_virtio_mapping_error, > + .max_mapping_size = rproc_virtio_max_mapping_size, > +}; > + > /* > * This function is called whenever vdev is released, and is responsible > * to decrement the remote processor's refcount which was taken when vdev was > @@ -355,6 +507,8 @@ static void rproc_virtio_dev_release(struct device *dev) > of_reserved_mem_device_release(&rvdev->pdev->dev); > dma_release_coherent_memory(&rvdev->pdev->dev); > > + kvfree(rvdev->map_records); > + > put_device(&rvdev->pdev->dev); > } > > @@ -429,13 +583,29 @@ static int rproc_add_virtio_dev(struct rproc_vdev > *rvdev, int id) > of_reserved_mem_device_init_by_idx(dev, np, 0); > } > > + /* Allocate one tracking record for each page of the device reserved > + * memory. Contiguous memory is not required for this array, which can > + * also be quite big (depending on the size of the coherent memory), so > + * let's use vmalloc for this allocation. > + */ > + rvdev->map_records = kvcalloc(dma_dev_coherent_size(dev) >> PAGE_SHIFT, > + sizeof(*rvdev->map_records), > + GFP_KERNEL); > + if (!rvdev->map_records) { > + dev_err(dev, "failed to allocate memory for map records\n"); > + return -ENOMEM; > + } > + > /* Allocate virtio device */ > vdev = kzalloc_obj(*vdev); > - if (!vdev) > + if (!vdev) { > + kvfree(rvdev->map_records); > return -ENOMEM; > + } > > vdev->id.device = id; > vdev->config = &rproc_virtio_config_ops; > + vdev->map = &rproc_virtio_map_ops; > vdev->dev.parent = dev; > vdev->dev.release = rproc_virtio_dev_release; > > diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h > index c3ba51fe9e54..2ff48b505ac0 100644 > --- a/include/linux/remoteproc.h > +++ b/include/linux/remoteproc.h > @@ -339,10 +339,23 @@ struct rproc_vring { > struct virtqueue *vq; > }; > > +/** > + * struct rproc_map_record - remoteproc map record > + * @original: original virtual address > + * @num: allocation size > + * @bounce: bounce buffer virtual address (NULL if not used) > + */ > +struct rproc_map_record { > + void *original; > + size_t size; > + void *bounce; > +}; > + > /** > * struct rproc_vdev - remoteproc state for a supported virtio device > * @subdev: handle for registering the vdev as a rproc subdevice > * @pdev: remoteproc virtio platform device > + * @map_records: array of map records > * @id: virtio device id (as in virtio_ids.h) > * @node: list node > * @rproc: the rproc handle > @@ -358,6 +371,7 @@ struct rproc_vdev { > unsigned int id; > struct list_head node; > struct rproc *rproc; > + struct rproc_map_record *map_records; > u32 rsc_offset; > u32 index; > unsigned int num_vrings; > > -- > 2.55.0 >
