dmaengine: doc: Add sections for per descriptor metadata support
Update the provider and client documentation with details about the metadata support. Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com> Reviewed-by: Tero Kristo <t-kristo@ti.com> Tested-by: Keerthy <j-keerthy@ti.com> Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com> Link: https://lore.kernel.org/r/20191223110458.30766-4-peter.ujfalusi@ti.com Signed-off-by: Vinod Koul <vkoul@kernel.org>
This commit is contained in:
parent
5fe4beaac2
commit
7d083ae983
|
@ -151,6 +151,93 @@ The details of these operations are:
|
||||||
Note that callbacks will always be invoked from the DMA
|
Note that callbacks will always be invoked from the DMA
|
||||||
engines tasklet, never from interrupt context.
|
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
|
4. Submit the transaction
|
||||||
|
|
||||||
Once the descriptor has been prepared and the callback information
|
Once the descriptor has been prepared and the callback information
|
||||||
|
|
|
@ -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)
|
(DMA_CYCLIC). Addresses pointing to a device's register (e.g. a FIFO)
|
||||||
are typically fixed.
|
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
|
Device operations
|
||||||
-----------------
|
-----------------
|
||||||
|
|
||||||
|
|
Loading…
Reference in a new issue