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-rw-r--r--Documentation/driver-api/dmaengine/client.rst14
1 files changed, 10 insertions, 4 deletions
diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst
index e5953e7e4bf4..2104830a99ae 100644
--- a/Documentation/driver-api/dmaengine/client.rst
+++ b/Documentation/driver-api/dmaengine/client.rst
@@ -151,8 +151,8 @@ The details of these operations are:
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
@@ -199,12 +199,15 @@ Optional: per descriptor metadata
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
@@ -215,6 +218,7 @@ Optional: per descriptor metadata
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
@@ -222,7 +226,9 @@ Optional: per descriptor metadata
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
@@ -278,8 +284,8 @@ Optional: per descriptor metadata
void dma_async_issue_pending(struct dma_chan *chan);
-Further APIs:
--------------
+Further APIs
+------------
1. Terminate APIs