linux-kernel - [PATCH v5 14/18] dmaengine: dma-jz4780: Further residue status fix

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Date:   Wed, 29 Aug 2018 23:32:56 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Vinod Koul <vkoul@...nel.org>, Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>
Cc:     od@...c.me, dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
        Daniel Silsby <dansilsby@...il.com>,
        Paul Cercueil <paul@...pouillou.net>
Subject: [PATCH v5 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>
---

Notes:
     v2: No change
    
     v3: No change
    
     v4: Add my Signed-off-by
    
     v5: No change

 drivers/dma/dma-jz4780.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
index d3b915ec8a09..b73d96166637 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