linux-kernel - [PATCH AUTOSEL 4.18 82/92] dmaengine: sh: rcar-dmac: avoid to write CHCR.TE to 1 if TCR is set to 0

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Date:   Sat, 15 Sep 2018 01:30:48 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Vinod Koul <vkoul@...nel.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 82/92] dmaengine: sh: rcar-dmac: avoid to write
 CHCR.TE to 1 if TCR is set to 0

From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>

[ Upstream commit 538603c6026ce769eec633bb79349f5f287519c7 ]

This patch fixes an issue that unexpected retransfering happens
if TCR is set to 0 before rcar_dmac_sync_tcr() writes DE bit to
the CHCR register. For example, sh-sci driver can reproduce this
issue like below:

 In rx_timer_fn():		/* CHCR DE bit may be set to 1 */
  dmaengine_tx_status()
   rcar_dmac_tx_status()
    rcar_dmac_chan_get_residue()
     rcar_dmac_sync_tcr()	/* TCR is possible to be set to 0 */

According to the description of commit 73a47bd0da66 ("dmaengine:
rcar-dmac: use TCRB instead of TCR for residue"), "this buffered data
will be transferred if CHCR::DE bit was cleared". So, this patch
doesn't need to check TCRB register.

Fixes: 73a47bd0da66 ("dmaengine: rcar-dmac: use TCRB instead of TCR for residue")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Signed-off-by: Vinod Koul <vkoul@...nel.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/dma/sh/rcar-dmac.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index 2a2ccd9c78e4..8305a1ce8a9b 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -774,8 +774,9 @@ static void rcar_dmac_sync_tcr(struct rcar_dmac_chan *chan)
 	/* make sure all remaining data was flushed */
 	rcar_dmac_chcr_de_barrier(chan);
 
-	/* back DE */
-	rcar_dmac_chan_write(chan, RCAR_DMACHCR, chcr);
+	/* back DE if remain data exists */
+	if (rcar_dmac_chan_read(chan, RCAR_DMATCR))
+		rcar_dmac_chan_write(chan, RCAR_DMACHCR, chcr);
 }
 
 static void rcar_dmac_chan_halt(struct rcar_dmac_chan *chan)
-- 
2.17.1