On 30-08-18, 15:19, Peter Ujfalusi wrote: > Update the provider and client documentation with details about the > metadata support.
It would make sense to make this patch 1 :) > > Signed-off-by: Peter Ujfalusi <[email protected]> > --- > Documentation/driver-api/dmaengine/client.rst | 70 +++++++++++++++++++ > .../driver-api/dmaengine/provider.rst | 46 ++++++++++++ > 2 files changed, 116 insertions(+) > > diff --git a/Documentation/driver-api/dmaengine/client.rst > b/Documentation/driver-api/dmaengine/client.rst > index fbbb2831f29f..584a39347cfe 100644 > --- a/Documentation/driver-api/dmaengine/client.rst > +++ b/Documentation/driver-api/dmaengine/client.rst > @@ -151,6 +151,76 @@ 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 > + --------------------------------- > + 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 > + 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 > + - 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 > + > + 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 are > + 4. Read out the metadate from the pointer Lets put a note here that only one method should be used > + > 4. Submit the transaction > > Once the descriptor has been prepared and the callback information > diff --git a/Documentation/driver-api/dmaengine/provider.rst > b/Documentation/driver-api/dmaengine/provider.rst > index dfc4486b5743..502c59f75302 100644 > --- a/Documentation/driver-api/dmaengine/provider.rst > +++ b/Documentation/driver-api/dmaengine/provider.rst > @@ -247,6 +247,52 @@ after each transfer. In case of a ring buffer, they may > loop > (DMA_CYCLIC). Addresses pointing to a device's register (e.g. a FIFO) > are typically fixed. > > +Per descriptor metadata support > +------------------------------- > +Some data movement architecure (DMA controller and peripherals) uses metadata typo architecure > +associated with a transaction. The DMA controller role is to transfer the > +payload and the metadata alongside. > +The metadata itself is not used by the DMA engine itself, but it contains > +parameters, keys, vectors, etc for peripheral or from the peripheral. > + > +The DMAengine framework provides a generic ways to facilitate the metadata > for > +descriptors. Depending on the architecture the DMA driver can implment either implment -- ~Vinod
