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[v2,12/15] dmaengine: Add provider documentation on cookie assignment

Message ID 20220503200728.2321188-13-benjamin.walker@intel.com (mailing list archive)
State Changes Requested
Headers show
Series dmaengine: Support polling for out of order completions | expand

Commit Message

Ben Walker May 3, 2022, 8:07 p.m. UTC
Clarify the rules on assigning cookies to DMA transactions.

Signed-off-by: Ben Walker <benjamin.walker@intel.com>
 .../driver-api/dmaengine/provider.rst         | 45 +++++++++++++++----
 1 file changed, 37 insertions(+), 8 deletions(-)
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diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
index e9e9de18d6b02..7c8ace703c96f 100644
--- a/Documentation/driver-api/dmaengine/provider.rst
+++ b/Documentation/driver-api/dmaengine/provider.rst
@@ -421,7 +421,9 @@  supported.
     - 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.
+      pending queue, waiting for issue_pending to be called. Each
+      descriptor is given a cookie to identify it. See the section
+      "Cookie Management" below.
   - In this structure the function pointer callback_result can be
     initialized in order for the submitter to be notified that a
@@ -526,6 +528,40 @@  supported.
   - May sleep.
+Cookie Management
+When a transaction is queued for submission via tx_submit(), the provider
+must assign that transaction a cookie (dma_cookie_t) to uniquely identify it.
+The provider is allowed to perform this assignment however it wants, but for
+convenience the following utility functions are available to create
+monotonically increasing cookies
+  .. code-block:: c
+    void dma_cookie_init(struct dma_chan *chan);
+  Called once at channel creation
+  .. code-block:: c
+    dma_cookie_t dma_cookie_assign(struct dma_async_tx_descriptor *tx);
+  Assign a cookie to the given descriptor
+  .. code-block:: c
+    void dma_cookie_complete(struct dma_async_tx_descriptor *tx);
+  Mark the descriptor as complete and invalidate the cookie
+  .. code-block:: c
+    enum dma_status dma_cookie_status(struct dma_chan *chan,
+      dma_cookie_t cookie, struct dma_tx_state *state);
+  Report the status of the cookie and filling in state, if not NULL.
 Misc notes
@@ -541,13 +577,6 @@  where to put them)
 - Makes sure that dependent operations are run before marking it
   as complete.
-- it's a DMA transaction ID.
-- The value can be chosen by the provider, or use the helper APIs
-  such as dma_cookie_assign() and dma_cookie_complete().
 - If clear, the descriptor cannot be reused by provider until the