On 20-12-19, 11:52, Peter Ujfalusi wrote: > Hi Vinod, > > On 20/12/2019 10.28, Vinod Koul wrote: > > 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? > > It is not defined as it could be driver dependent, but afaik we have > defined (which I'm not sure why it is not here or in the code) that in > DESC_METADATA_ENGINE case the metadata pointer is valid for the client > between the time it got the desc (via prep call) and the execution of > the completion callback. > Iow, DESC_METADATA_ENGINE does not make any sense if the client want to > receive metadata back and does not provide a callback. Make sense and once callback completes driver can free it up! > > I will extend the documentation and comment in the code to reflect this. makes sense, thanks! > > >> + 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? > > It is up to the client driver what it does with the provided buffer. As > for what the DMA driver does is not documented as it is not relevant and > can be different by different HW or SW implementation. yeah lets document that and the fact the dmaengine driver cant touch it after the callback -- ~Vinod
