linux-kernel - [PATCH] rcar-dmac: fixup descriptor pointer for descriptor mode

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Date:   Tue, 23 May 2017 07:08:43 +0000
From:   Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Vinod Koul <vinod.koul@...el.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
CC:     <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] rcar-dmac: fixup descriptor pointer for descriptor mode


From: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>

In descriptor mode, the descriptor running pointer is not maintained
by the interrupt handler, thus, driver finds the running descriptor
from the descriptor pointer field in the CHCRB register.
But, CHCRB::DPTR indicates *next* descriptor pointer, not current.
Thus, The residue calculation will be missed. This patch fixup it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
---
 drivers/dma/sh/rcar-dmac.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index d2cb4a0..ffcadca 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1293,6 +1293,9 @@ static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 	if (desc->hwdescs.use) {
 		dptr = (rcar_dmac_chan_read(chan, RCAR_DMACHCRB) &
 			RCAR_DMACHCRB_DPTR_MASK) >> RCAR_DMACHCRB_DPTR_SHIFT;
+		if (dptr == 0)
+			dptr = desc->nchunks;
+		dptr--;
 		WARN_ON(dptr >= desc->nchunks);
 	} else {
 		running = desc->running;
-- 
1.9.1