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

From: Ben Walker <benjamin.walker@intel.com>
To: vkoul@kernel.org
Cc: dmaengine@vger.kernel.org, herbert@gondor.apana.org.au,
	davem@davemloft.net, mchehab@kernel.org,
	mporter@kernel.crashing.org, alex.bou9@gmail.com,
	Ben Walker <benjamin.walker@intel.com>
Subject: [PATCH v2 12/15] dmaengine: Add provider documentation on cookie assignment
Date: Tue,  3 May 2022 13:07:25 -0700	[thread overview]
Message-ID: <20220503200728.2321188-13-benjamin.walker@intel.com> (raw)
In-Reply-To: <20220503200728.2321188-1-benjamin.walker@intel.com>

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(-)

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.
 
-dma_cookie_t
-
-- 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().
-
 DMA_CTRL_ACK
 
 - If clear, the descriptor cannot be reused by provider until the
-- 
2.35.1

