Note that callbacks will always be invoked from the DMA
engines tasklet, never from interrupt context.
-Optional: per descriptor metadata
----------------------------------
+ **Optional: per descriptor metadata**
+
DMAengine provides two ways for metadata support.
DESC_METADATA_CLIENT
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
+
- DMA_DEV_TO_MEM:
+
1. prepare the descriptor (dmaengine_prep_*)
2. use dmaengine_desc_attach_metadata() to attach the buffer to the
descriptor
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
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
void dma_async_issue_pending(struct dma_chan *chan);
-Further APIs:
--------------
+Further APIs
+------------
1. Terminate APIs