Hi Peter, On 09-12-19, 11:43, Peter Ujfalusi wrote: > + Optional: per descriptor metadata > + --------------------------------- > + DMAengine provides two ways for metadata support. > + > + DESC_METADATA_CLIENT > + > + The metadata buffer is allocated/provided by the client driver and it is > + attached to the descriptor. > + > + .. code-block:: c > + > + int dmaengine_desc_attach_metadata(struct dma_async_tx_descriptor *desc, > + void *data, size_t len); > + > + DESC_METADATA_ENGINE > + > + The metadata buffer is allocated/managed by the DMA driver. The client and when would it be freed? > + driver can ask for the pointer, maximum size and the currently used size of > + the metadata and can directly update or read it. > + > + .. code-block:: c > + > + void *dmaengine_desc_get_metadata_ptr(struct dma_async_tx_descriptor *desc, > + size_t *payload_len, size_t *max_len); > + > + int dmaengine_desc_set_metadata_len(struct dma_async_tx_descriptor *desc, > + size_t payload_len); > + > + Client drivers can query if a given mode is supported with: > + > + .. code-block:: c > + > + bool dmaengine_is_metadata_mode_supported(struct dma_chan *chan, > + enum dma_desc_metadata_mode mode); > + > + Depending on the used mode client drivers must follow different flow. > + > + DESC_METADATA_CLIENT > + > + - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM: > + 1. prepare the descriptor (dmaengine_prep_*) > + construct the metadata in the client's buffer > + 2. use dmaengine_desc_attach_metadata() to attach the buffer to the > + descriptor > + 3. submit the transfer This is simpler, txn finished the metadata would be freed up right? > + - DMA_DEV_TO_MEM: > + 1. prepare the descriptor (dmaengine_prep_*) > + 2. use dmaengine_desc_attach_metadata() to attach the buffer to the > + descriptor > + 3. submit the transfer > + 4. when the transfer is completed, the metadata should be available in the > + attached buffer and when and how would driver free that up :) > + > + DESC_METADATA_ENGINE > + > + - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM: > + 1. prepare the descriptor (dmaengine_prep_*) > + 2. use dmaengine_desc_get_metadata_ptr() to get the pointer to the > + engine's metadata area > + 3. update the metadata at the pointer > + 4. use dmaengine_desc_set_metadata_len() to tell the DMA engine the > + amount of data the client has placed into the metadata buffer > + 5. submit the transfer > + - DMA_DEV_TO_MEM: > + 1. prepare the descriptor (dmaengine_prep_*) > + 2. submit the transfer > + 3. on transfer completion, use dmaengine_desc_get_metadata_ptr() to get the > + pointer to the engine's metadata area > + 4. Read out the metadata from the pointer > + > + .. note:: > + > + Mixed use of DESC_METADATA_CLIENT / DESC_METADATA_ENGINE is not allowed, > + client drivers must use either of the modes per descriptor. We should check that if not done already! -- ~Vinod
