[PATCH 4.4 035/159] dmaengine: dma-jz4780: Further residue status fix

From: Greg Kroah-Hartman
Date: Fri Nov 22 2019 - 06:26:21 EST

From: Daniel Silsby <dansilsby@xxxxxxxxx>

[ Upstream commit 83ef4fb7556b6a673f755da670cbacab7e2c7f1b ]

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@xxxxxxxxx>
Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
Tested-by: Mathieu Malaterre <malat@xxxxxxxxxx>
Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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 8344b7c91fe35..1d01e3805f9c2 100644
--- a/drivers/dma/dma-jz4780.c
+++ b/drivers/dma/dma-jz4780.c
@@ -576,7 +576,7 @@ 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;