linux-kernel - [PATCH v4 14/18] dmaengine: dma-jz4780: Further residue status fix

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Date:   Tue,  7 Aug 2018 13:42:14 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Vinod Koul <vkoul@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Zubair Lutfullah Kakakhel <Zubair.Kakakhel@...tec.com>
Cc:     Paul Cercueil <paul@...pouillou.net>, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mips@...ux-mips.org, Daniel Silsby <dansilsby@...il.com>
Subject: [PATCH v4 14/18] dmaengine: dma-jz4780: Further residue status fix

From: Daniel Silsby <dansilsby@...il.com>

Func jz4780_dma_desc_residue() expects the index to the next hw
descriptor as its last parameter. Caller func jz4780_dma_tx_status(),
however, applied modulus before passing it. When the current hw
descriptor was last in the list, the index passed became zero.

The resulting excess of reported residue especially caused problems
with cyclic DMA transfer clients, i.e. ALSA AIC audio output, which
rely on this for determining current DMA location within buffer.

Combined with the recent and related residue-reporting fixes, spurious
ALSA audio underruns on jz4770 hardware are now fixed.

Signed-off-by: Daniel Silsby <dansilsby@...il.com>
Signed-off-by: Paul Cercueil <paul@...pouillou.net>
Tested-by: Mathieu Malaterre <malat@...ian.org>
---
 drivers/dma/dma-jz4780.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

 v2: No change

 v3: No change

 v4: Add my Signed-off-by

diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
index d03711834a44..351dc8268515 100644
--- a/drivers/dma/dma-jz4780.c
+++ b/drivers/dma/dma-jz4780.c
@@ -653,7 +653,7 @@ static enum dma_status jz4780_dma_tx_status(struct dma_chan *chan,
 					to_jz4780_dma_desc(vdesc), 0);
 	} else if (cookie == jzchan->desc->vdesc.tx.cookie) {
 		txstate->residue = jz4780_dma_desc_residue(jzchan, jzchan->desc,
-			  (jzchan->curr_hwdesc + 1) % jzchan->desc->count);
+					jzchan->curr_hwdesc + 1);
 	} else
 		txstate->residue = 0;
 
-- 
2.11.0