diff mbox series

[v3,2/2] dmaengine: sh: rcar-dmac: Fix glitch in dmaengine_tx_status

Message ID 20190412052914.16006-2-dirk.behme@de.bosch.com (mailing list archive)
State Accepted
Delegated to: Geert Uytterhoeven
Headers show
Series [v3,1/2] dmaengine: sh: rcar-dmac: With cyclic DMA residue 0 is valid | expand

Commit Message

Dirk Behme April 12, 2019, 5:29 a.m. UTC 
From: Achim Dahlhoff <Achim.Dahlhoff@de.bosch.com>

The tx_status poll in the rcar_dmac driver reads the status register
which indicates which chunk is busy (DMACHCRB). Afterwards the point
inside the chunk is read from DMATCRB. It is possible that the chunk
has changed between the two reads. The result is a non-monotonous
increase of the residue. Fix this by introducing a 'safe read' logic.

Fixes: 73a47bd0da66 ("dmaengine: rcar-dmac: use TCRB instead of TCR for residue")
Signed-off-by: Achim Dahlhoff <Achim.Dahlhoff@de.bosch.com>
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Cc: <stable@vger.kernel.org> # v4.16+
---
Note: Patch done against mainline v5.0

Changes in v2: Switch goto/retry to for loop

Changes in v3: None

 drivers/dma/sh/rcar-dmac.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

Comments

Yoshihiro Shimoda April 12, 2019, 8:52 a.m. UTC | #1 
Hi Dirk-san,

> From: Dirk Behme, Sent: Friday, April 12, 2019 2:29 PM
> 
> From: Achim Dahlhoff <Achim.Dahlhoff@de.bosch.com>
> 
> The tx_status poll in the rcar_dmac driver reads the status register
> which indicates which chunk is busy (DMACHCRB). Afterwards the point
> inside the chunk is read from DMATCRB. It is possible that the chunk
> has changed between the two reads. The result is a non-monotonous
> increase of the residue. Fix this by introducing a 'safe read' logic.
> 
> Fixes: 73a47bd0da66 ("dmaengine: rcar-dmac: use TCRB instead of TCR for residue")

I guess this driver has this issue potencially from previous of the commit
(maybe commit ccadee9b1e9 ("dmaengine: rcar-dmac: Implement support for hardware descriptor lists"?).

But, this patch seems good to fix the issue.
So,

Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>

Best regards,
Yoshihiro Shimoda
diff mbox series

Patch

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index 54810ffd95e2..e2a5398f89b5 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1282,6 +1282,9 @@  static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 	enum dma_status status;
 	unsigned int residue = 0;
 	unsigned int dptr = 0;
+	unsigned int chcrb;
+	unsigned int tcrb;
+	unsigned int i;
 
 	if (!desc)
 		return 0;
@@ -1329,6 +1332,24 @@  static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 		return 0;
 	}
 
+	/*
+	 * We need to read two registers.
+	 * Make sure the control register does not skip to next chunk
+	 * while reading the counter.
+	 * Trying it 3 times should be enough: Initial read, retry, retry
+	 * for the paranoid.
+	 */
+	for (i = 0; i < 3; i++) {
+		chcrb = rcar_dmac_chan_read(chan, RCAR_DMACHCRB) &
+					    RCAR_DMACHCRB_DPTR_MASK;
+		tcrb = rcar_dmac_chan_read(chan, RCAR_DMATCRB);
+		/* Still the same? */
+		if (chcrb == (rcar_dmac_chan_read(chan, RCAR_DMACHCRB) &
+			      RCAR_DMACHCRB_DPTR_MASK))
+			break;
+	}
+	WARN_ONCE(i >= 3, "residue might be not continuous!");
+
 	/*
 	 * In descriptor mode the descriptor running pointer is not maintained
 	 * by the interrupt handler, find the running descriptor from the
@@ -1336,8 +1357,7 @@  static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 	 * mode just use the running descriptor pointer.
 	 */
 	if (desc->hwdescs.use) {
-		dptr = (rcar_dmac_chan_read(chan, RCAR_DMACHCRB) &
-			RCAR_DMACHCRB_DPTR_MASK) >> RCAR_DMACHCRB_DPTR_SHIFT;
+		dptr = chcrb >> RCAR_DMACHCRB_DPTR_SHIFT;
 		if (dptr == 0)
 			dptr = desc->nchunks;
 		dptr--;
@@ -1355,7 +1375,7 @@  static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 	}
 
 	/* Add the residue for the current chunk. */
-	residue += rcar_dmac_chan_read(chan, RCAR_DMATCRB) << desc->xfer_shift;
+	residue += tcrb << desc->xfer_shift;
 
 	return residue;
 }