Update the provider and client documentation with details about the
metadata support.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
Reviewed-by: Tero Kristo <t-kristo@xxxxxx>
Tested-by: Keerthy <j-keerthy@xxxxxx>
Reviewed-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
---
Documentation/driver-api/dmaengine/client.rst | 87 +++++++++++++++++++
.../driver-api/dmaengine/provider.rst | 48 ++++++++++
2 files changed, 135 insertions(+)
diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst
index 45953f171500..a9a7a3c84c63 100644
--- a/Documentation/driver-api/dmaengine/client.rst
+++ b/Documentation/driver-api/dmaengine/client.rst
@@ -151,6 +151,93 @@ 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.
+
+ Becasue the DMA driver manages the memory area containing the metadata,
+ clients must make sure that they do not try to access or get the pointer
+ after their transfer completion callback has run for the descriptor.
+ If no completion callback has been defined for the transfer, then the
+ metadata must not be accessed after issue_pending.
+ In other words: if the aim is to read back metadata after the transfer is
+ completed, then the client must use completion callback.
+
+ .. 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 area
+ 4. read out the metadata from the pointer
+
+ .. note::
+
+ When DESC_METADATA_ENGINE mode is used the metadata area for the descriptor
+ is no longer valid after the transfer has been completed (valid up to the
+ point when the completion callback returns if used).
+
+ Mixed use of DESC_METADATA_CLIENT / DESC_METADATA_ENGINE is not allowed,
+ client drivers must use either of the modes per descriptor.
+
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..790a15089f1f 100644
--- a/Documentation/driver-api/dmaengine/provider.rst
+++ b/Documentation/driver-api/dmaengine/provider.rst
@@ -247,6 +247,54 @@ 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 architecture (DMA controller and peripherals) uses metadata
+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 implement either
+or both of the methods and it is up to the client driver to choose which one
+to use.
+
+- DESC_METADATA_CLIENT
+
+ The metadata buffer is allocated/provided by the client driver and it is
+ attached (via the dmaengine_desc_attach_metadata() helper to the descriptor.
+
+ From the DMA driver the following is expected for this mode:
+ - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM
+ The data from the provided metadata buffer should be prepared for the DMA
+ controller to be sent alongside of the payload data. Either by copying to a
+ hardware descriptor, or highly coupled packet.
+ - DMA_DEV_TO_MEM
+ On transfer completion the DMA driver must copy the metadata to the client
+ provided metadata buffer before notifying the client about the completion.
+ After the transfer completion, DMA drivers must not touch the metadata
+ buffer provided by the client.
+
+- 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. dmaengine_desc_get_metadata_ptr()
+ and dmaengine_desc_set_metadata_len() is provided as helper functions.
+
+ From the DMA driver the following is expected for this mode:
+ - get_metadata_ptr
+ Should return a pointer for the metadata buffer, the maximum size of the
+ metadata buffer and the currently used / valid (if any) bytes in the buffer.
+ - set_metadata_len
+ It is called by the clients after it have placed the metadata to the buffer
+ to let the DMA driver know the number of valid bytes provided.
+
+ Note: since the client will ask for the metadata pointer in the completion
+ callback (in DMA_DEV_TO_MEM case) the DMA driver must ensure that the
+ descriptor is not freed up prior the callback is called.
+
Device operations
-----------------
--
Peter
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
