linux-kernel - [PATCH 4.9 40/44] dmaengine: bcm2835: Fix cyclic DMA period splitting

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Date:   Tue, 27 Jun 2017 16:12:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Matthias Reichl <hias@...us.com>,
        Martin Sperl <kernel@...tin.sperl.org>,
        Clive Messer <clive.messer@...italdreamtime.co.uk>,
        Eric Anholt <eric@...olt.net>,
        Vinod Koul <vinod.koul@...el.com>,
        Amit Pundir <amit.pundir@...aro.org>
Subject: [PATCH 4.9 40/44] dmaengine: bcm2835: Fix cyclic DMA period splitting

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthias Reichl <hias@...us.com>

commit 2201ac6129fa162ac24da089a034bb0971648ebb upstream.

The code responsible for splitting periods into chunks that
can be handled by the DMA controller missed to update total_len,
the number of bytes processed in the current period, when there
are more chunks to follow.

Therefore total_len was stuck at 0 and the code didn't work at all.
This resulted in a wrong control block layout and audio issues because
the cyclic DMA callback wasn't executing on period boundaries.

Fix this by adding the missing total_len update.

Signed-off-by: Matthias Reichl <hias@...us.com>
Signed-off-by: Martin Sperl <kernel@...tin.sperl.org>
Tested-by: Clive Messer <clive.messer@...italdreamtime.co.uk>
Reviewed-by: Eric Anholt <eric@...olt.net>
Signed-off-by: Vinod Koul <vinod.koul@...el.com>
Signed-off-by: Amit Pundir <amit.pundir@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/dma/bcm2835-dma.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/dma/bcm2835-dma.c
+++ b/drivers/dma/bcm2835-dma.c
@@ -251,8 +251,11 @@ static void bcm2835_dma_create_cb_set_le
 	 */
 
 	/* have we filled in period_length yet? */
-	if (*total_len + control_block->length < period_len)
+	if (*total_len + control_block->length < period_len) {
+		/* update number of bytes in this period so far */
+		*total_len += control_block->length;
 		return;
+	}
 
 	/* calculate the length that remains to reach period_length */
 	control_block->length = period_len - *total_len;