dmaengine: doc: ReSTize provider doc

This moves and converts provider file with some format changes
for RST style
Signed-off-by: NVinod Koul <vinod.koul@intel.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/driver-api/dmaengine/index.rst

@@ -5,6 +5,17 @@ DMAEngine documentation
 DMAEngine documentation provides documents for various aspects of DMAEngine
 framework.
 
+DMAEngine documentation
+-----------------------
+
+This book helps with DMAengine internal APIs and guide for DMAEngine device
+driver writers.
+
+.. toctree::
+   :maxdepth: 1
+
+   provider
+
 .. only::  subproject
 
    Indices

Documentation/dmaengine/provider.txt → Documentation/driver-api/dmaengine/provider.rst

+==================================
 DMAengine controller documentation
 ==================================
 
 Hardware Introduction
-+++++++++++++++++++++
+=====================
 
 Most of the Slave DMA controllers have the same general principles of
 operations.
@@ -81,7 +82,7 @@ support other kind of transfers or memory operations that dmaengine
 support and will be detailed later in this document.
 
 DMA Support in Linux
-++++++++++++++++++++
+====================
 
 Historically, DMA controller drivers have been implemented using the
 async TX API, to offload operations such as memory copy, XOR,
@@ -96,11 +97,11 @@ ensure that it stayed compatible.
 For more information on the Async TX API, please look the relevant
 documentation file in Documentation/crypto/async-tx-api.txt.
 
-DMAEngine Registration
-++++++++++++++++++++++
+DMAEngine APIs
+==============
 
-struct dma_device Initialization
---------------------------------
+``struct dma_device`` Initialization
+------------------------------------
 
 Just like any other kernel framework, the whole DMAEngine registration
 relies on the driver filling a structure and registering against the
@@ -110,35 +111,39 @@ The first thing you need to do in your driver is to allocate this
 structure. Any of the usual memory allocators will do, but you'll also
 need to initialize a few fields in there:
 
-  * channels:	should be initialized as a list using the
+- channels: should be initialized as a list using the
   INIT_LIST_HEAD macro for example
 
-  * src_addr_widths:
-    - should contain a bitmask of the supported source transfer width
+- src_addr_widths:
+  should contain a bitmask of the supported source transfer width
 
-  * dst_addr_widths:
-    - should contain a bitmask of the supported destination transfer
-      width
+- dst_addr_widths:
+  should contain a bitmask of the supported destination transfer width
 
-  * directions:
-    - should contain a bitmask of the supported slave directions
+- directions:
+  should contain a bitmask of the supported slave directions
   (i.e. excluding mem2mem transfers)
 
-  * residue_granularity:
+- residue_granularity:
+
   - Granularity of the transfer residue reported to dma_set_residue.
-    - This can be either:
-      + Descriptor
-        -> Your device doesn't support any kind of residue
+    This can be either:
+
+  - Descriptor
+
+    - Your device doesn't support any kind of residue
       reporting. The framework will only know that a particular
       transaction descriptor is done.
-      + Segment
-        -> Your device is able to report which chunks have been
-           transferred
-      + Burst
-        -> Your device is able to report which burst have been
-           transferred
-
-  * dev: 	should hold the pointer to the struct device associated
+
+      - Segment
+
+        - Your device is able to report which chunks have been transferred
+
+      - Burst
+
+        - Your device is able to report which burst have been transferred
+
+  - dev: should hold the pointer to the ``struct device`` associated
     to your current driver instance.
 
 Supported transaction types
@@ -147,72 +152,93 @@ Supported transaction types
 The next thing you need is to set which transaction types your device
 (and driver) supports.
 
-Our dma_device structure has a field called cap_mask that holds the
+Our ``dma_device structure`` has a field called cap_mask that holds the
 various types of transaction supported, and you need to modify this
 mask using the dma_cap_set function, with various flags depending on
 transaction types you support as an argument.
 
-All those capabilities are defined in the dma_transaction_type enum,
-in include/linux/dmaengine.h
+All those capabilities are defined in the ``dma_transaction_type enum``,
+in ``include/linux/dmaengine.h``
 
 Currently, the types available are:
-  * DMA_MEMCPY
+
+- DMA_MEMCPY
+
   - The device is able to do memory to memory copies
 
-  * DMA_XOR
+- DMA_XOR
+
   - The device is able to perform XOR operations on memory areas
+
   - Used to accelerate XOR intensive tasks, such as RAID5
 
-  * DMA_XOR_VAL
+- DMA_XOR_VAL
+
   - The device is able to perform parity check using the XOR
     algorithm against a memory buffer.
 
-  * DMA_PQ
+- DMA_PQ
+
   - The device is able to perform RAID6 P+Q computations, P being a
     simple XOR, and Q being a Reed-Solomon algorithm.
 
-  * DMA_PQ_VAL
+- DMA_PQ_VAL
+
   - The device is able to perform parity check using RAID6 P+Q
     algorithm against a memory buffer.
 
-  * DMA_INTERRUPT
+- DMA_INTERRUPT
+
   - The device is able to trigger a dummy transfer that will
     generate periodic interrupts
+
   - Used by the client drivers to register a callback that will be
     called on a regular basis through the DMA controller interrupt
 
-  * DMA_PRIVATE
+- DMA_PRIVATE
+
   - The devices only supports slave transfers, and as such isn't
     available for async transfers.
 
-  * DMA_ASYNC_TX
+- DMA_ASYNC_TX
+
   - Must not be set by the device, and will be set by the framework
     if needed
-    - /* TODO: What is it about? */
 
-  * DMA_SLAVE
+  - TODO: What is it about?
+
+- DMA_SLAVE
+
   - The device can handle device to memory transfers, including
     scatter-gather transfers.
+
   - While in the mem2mem case we were having two distinct types to
     deal with a single chunk to copy or a collection of them, here,
     we just have a single transaction type that is supposed to
     handle both.
+
   - If you want to transfer a single contiguous memory buffer,
     simply build a scatter list with only one item.
 
-  * DMA_CYCLIC
+- DMA_CYCLIC
+
   - The device can handle cyclic transfers.
+
   - A cyclic transfer is a transfer where the chunk collection will
     loop over itself, with the last item pointing to the first.
+
   - It's usually used for audio transfers, where you want to operate
     on a single ring buffer that you will fill with your audio data.
 
-  * DMA_INTERLEAVE
+- DMA_INTERLEAVE
+
   - The device supports interleaved transfer.
+
   - These transfers can transfer data from a non-contiguous buffer
     to a non-contiguous buffer, opposed to DMA_SLAVE that can
     transfer data from a non-contiguous data set to a continuous
     destination buffer.
+
   - It's usually used for 2d content transfers, in which case you
     want to transfer a portion of uncompressed data directly to the
     display to print it
@@ -236,168 +262,225 @@ The functions that we have to fill in there, and hence have to
 implement, obviously depend on the transaction types you reported as
 supported.
 
-   * device_alloc_chan_resources
-   * device_free_chan_resources
+- ``device_alloc_chan_resources``
+
+- ``device_free_chan_resources``
+
   - These functions will be called whenever a driver will call
-       dma_request_channel or dma_release_channel for the first/last
+    ``dma_request_channel`` or ``dma_release_channel`` for the first/last
     time on the channel associated to that driver.
+
   - They are in charge of allocating/freeing all the needed
-       resources in order for that channel to be useful for your
-       driver.
+    resources in order for that channel to be useful for your driver.
+
   - These functions can sleep.
 
-   * device_prep_dma_*
+- ``device_prep_dma_*``
+
   - These functions are matching the capabilities you registered
     previously.
+
   - These functions all take the buffer or the scatterlist relevant
     for the transfer being prepared, and should create a hardware
     descriptor or a list of hardware descriptors from it
+
   - These functions can be called from an interrupt context
+
   - Any allocation you might do should be using the GFP_NOWAIT
     flag, in order not to potentially sleep, but without depleting
     the emergency pool either.
+
   - Drivers should try to pre-allocate any memory they might need
     during the transfer setup at probe time to avoid putting to
     much pressure on the nowait allocator.
 
   - It should return a unique instance of the
-       dma_async_tx_descriptor structure, that further represents this
+    ``dma_async_tx_descriptor structure``, that further represents this
     particular transfer.
 
   - This structure can be initialized using the function
-       dma_async_tx_descriptor_init.
+    ``dma_async_tx_descriptor_init``.
+
   - You'll also need to set two fields in this structure:
-       + flags:
+
+    - flags:
       TODO: Can it be modified by the driver itself, or
       should it be always the flags passed in the arguments
 
-       + tx_submit:	A pointer to a function you have to implement,
-			that is supposed to push the current
-			transaction descriptor to a pending queue, waiting
-			for issue_pending to be called.
+    - tx_submit: A pointer to a function you have to implement,
+      that is supposed to push the current transaction descriptor to a
+      pending queue, waiting for issue_pending to be called.
+
   - In this structure the function pointer callback_result can be
     initialized in order for the submitter to be notified that a
     transaction has completed. In the earlier code the function pointer
     callback has been used. However it does not provide any status to the
     transaction and will be deprecated. The result structure defined as
-       dmaengine_result that is passed in to callback_result has two fields:
-       + result: This provides the transfer result defined by
-		 dmaengine_tx_result. Either success or some error
-		 condition.
-       + residue: Provides the residue bytes of the transfer for those that
+    ``dmaengine_result`` that is passed in to callback_result
+    has two fields:
+
+    - result: This provides the transfer result defined by
+      ``dmaengine_tx_result``. Either success or some error condition.
+
+    - residue: Provides the residue bytes of the transfer for those that
       support residue.
 
-   * device_issue_pending
+- ``device_issue_pending``
+
   - Takes the first transaction descriptor in the pending queue,
     and starts the transfer. Whenever that transfer is done, it
     should move to the next transaction in the list.
+
   - This function can be called in an interrupt context
 
-   * device_tx_status
+- ``device_tx_status``
+
   - Should report the bytes left to go over on the given channel
+
   - Should only care about the transaction descriptor passed as
     argument, not the currently active one on a given channel
+
   - The tx_state argument might be NULL
+
   - Should use dma_set_residue to report it
+
   - In the case of a cyclic transfer, it should only take into
     account the current period.
+
   - This function can be called in an interrupt context.
 
-   * device_config
-     - Reconfigures the channel with the configuration given as
-       argument
+- device_config
+
+  - Reconfigures the channel with the configuration given as argument
+
   - This command should NOT perform synchronously, or on any
     currently queued transfers, but only on subsequent ones
-     - In this case, the function will receive a dma_slave_config
+
+  - In this case, the function will receive a ``dma_slave_config``
     structure pointer as an argument, that will detail which
     configuration to use.
+
   - Even though that structure contains a direction field, this
     field is deprecated in favor of the direction argument given to
     the prep_* functions
+
   - This call is mandatory for slave operations only. This should NOT be
     set or expected to be set for memcpy operations.
     If a driver support both, it should use this call for slave
     operations only and not for memcpy ones.
 
-   * device_pause
+- device_pause
+
   - Pauses a transfer on the channel
+
   - This command should operate synchronously on the channel,
     pausing right away the work of the given channel
 
-   * device_resume
+- device_resume
+
   - Resumes a transfer on the channel
+
   - This command should operate synchronously on the channel,
     resuming right away the work of the given channel
 
-   * device_terminate_all
+- device_terminate_all
+
   - Aborts all the pending and ongoing transfers on the channel
+
   - For aborted transfers the complete callback should not be called
+
   - Can be called from atomic context or from within a complete
     callback of a descriptor. Must not sleep. Drivers must be able
     to handle this correctly.
+
   - Termination may be asynchronous. The driver does not have to
     wait until the currently active transfer has completely stopped.
     See device_synchronize.
 
-   * device_synchronize
+- device_synchronize
+
   - Must synchronize the termination of a channel to the current
     context.
+
   - Must make sure that memory for previously submitted
     descriptors is no longer accessed by the DMA controller.
+
   - Must make sure that all complete callbacks for previously
     submitted descriptors have finished running and none are
     scheduled to run.
+
   - May sleep.
 
 
-Misc notes (stuff that should be documented, but don't really know
+Misc notes
+==========
+
+(stuff that should be documented, but don't really know
 where to put them)
-------------------------------------------------------------------
-  * dma_run_dependencies
-    - Should be called at the end of an async TX transfer, and can be
+
+``dma_run_dependencies``
+
+- Should be called at the end of an async TX transfer, and can be
   ignored in the slave transfers case.
-    - Makes sure that dependent operations are run before marking it
+
+- Makes sure that dependent operations are run before marking it
   as complete.
 
-  * dma_cookie_t
-    - it's a DMA transaction ID that will increment over time.
-    - Not really relevant any more since the introduction of virt-dma
+dma_cookie_t
+
+- it's a DMA transaction ID that will increment over time.
+
+- Not really relevant any more since the introduction of ``virt-dma``
   that abstracts it away.
 
-  * DMA_CTRL_ACK
-    - If clear, the descriptor cannot be reused by provider until the
+DMA_CTRL_ACK
+
+- If clear, the descriptor cannot be reused by provider until the
   client acknowledges receipt, i.e. has has a chance to establish any
   dependency chains
-    - This can be acked by invoking async_tx_ack()
-    - If set, does not mean descriptor can be reused
 
-  * DMA_CTRL_REUSE
-    - If set, the descriptor can be reused after being completed. It should
+- This can be acked by invoking async_tx_ack()
+
+- If set, does not mean descriptor can be reused
+
+DMA_CTRL_REUSE
+
+- If set, the descriptor can be reused after being completed. It should
   not be freed by provider if this flag is set.
-    - The descriptor should be prepared for reuse by invoking
-      dmaengine_desc_set_reuse() which will set DMA_CTRL_REUSE.
-    - dmaengine_desc_set_reuse() will succeed only when channel support
+
+- The descriptor should be prepared for reuse by invoking
+  ``dmaengine_desc_set_reuse()`` which will set DMA_CTRL_REUSE.
+
+- ``dmaengine_desc_set_reuse()`` will succeed only when channel support
   reusable descriptor as exhibited by capabilities
-    - As a consequence, if a device driver wants to skip the dma_map_sg() and
-      dma_unmap_sg() in between 2 transfers, because the DMA'd data wasn't used,
-      it can resubmit the transfer right after its completion.
-    - Descriptor can be freed in few ways
-	- Clearing DMA_CTRL_REUSE by invoking dmaengine_desc_clear_reuse()
-	  and submitting for last txn
-	- Explicitly invoking dmaengine_desc_free(), this can succeed only
+
+- As a consequence, if a device driver wants to skip the
+  ``dma_map_sg()`` and ``dma_unmap_sg()`` in between 2 transfers,
+  because the DMA'd data wasn't used, it can resubmit the transfer right after
+  its completion.
+
+- Descriptor can be freed in few ways
+
+  - Clearing DMA_CTRL_REUSE by invoking
+    ``dmaengine_desc_clear_reuse()`` and submitting for last txn
+
+  - Explicitly invoking ``dmaengine_desc_free()``, this can succeed only
     when DMA_CTRL_REUSE is already set
+
   - Terminating the channel
 
-  * DMA_PREP_CMD
+- DMA_PREP_CMD
+
   - If set, the client driver tells DMA controller that passed data in DMA
     API is command data.
+
   - Interpretation of command data is DMA controller specific. It can be
     used for issuing commands to other peripherals/register reads/register
     writes for which the descriptor should be in different format from
     normal data descriptors.
 
 General Design Notes
---------------------
+====================
 
 Most of the DMAEngine drivers you'll see are based on a similar design
 that handles the end of transfer interrupts in the handler, but defer
@@ -415,10 +498,11 @@ order to have a shorter idle window (that we can't really avoid
 anyway).
 
 Glossary
---------
+========
+
+- Burst: A number of consecutive read or write operations that
+  can be queued to buffers before being flushed to memory.
+
+- Chunk: A contiguous collection of bursts
 
-Burst: 		A number of consecutive read or write operations
-		that can be queued to buffers before being flushed to
-		memory.
-Chunk:		A contiguous collection of bursts
-Transfer:	A collection of chunks (be it contiguous or not)
+- Transfer: A collection of chunks (be it contiguous or not)