linux-kernel - [PATCH] dmaengine: Clarify cyclic transfer residue documentation

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Date:   Thu, 31 Mar 2022 15:41:14 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     dmaengine@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Vinod Koul <vkoul@...nel.org>, Jonathan Corbet <corbet@....net>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: [PATCH] dmaengine: Clarify cyclic transfer residue documentation

The current documentation for the residue reported in a cyclic transfer
case mentions that the reported residue should be relative to the current
period only. However the definition of DMA_RESIDUE_GRANULARITY_SEGMENT
specifies that the residue should be updated after each period for
a cyclic transfer, which is in direct contradiction.

Moreover the pcm_dmaengine common code uses the residue relative to
the whole cyclic buffer size, not one period.

Correct the residue-related documentation to reflect this.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
---
 Documentation/driver-api/dmaengine/provider.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
index 0072c9c7efd3..d3fa80e333b1 100644
--- a/Documentation/driver-api/dmaengine/provider.rst
+++ b/Documentation/driver-api/dmaengine/provider.rst
@@ -457,7 +457,7 @@ supported.
   - Should use dma_set_residue to report it
 
   - In the case of a cyclic transfer, it should only take into
-    account the current period.
+    account the total size of the cyclic buffer.
 
   - Should return DMA_OUT_OF_ORDER if the device does not support in order
     completion and is completing the operation out of order.
-- 
2.35.1