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From:   Philipp Puschmann <philipp.puschmann@emlix.com>
To:     linux-kernel@vger.kernel.org
Cc:     yibin.gong@nxp.com, fugang.duan@nxp.com, l.stach@pengutronix.de,
        dan.j.williams@intel.com, vkoul@kernel.org, shawnguo@kernel.org,
        s.hauer@pengutronix.de, kernel@pengutronix.de, festevam@gmail.com,
        linux-imx@nxp.com, dmaengine@vger.kernel.or,
        linux-arm-kernel@lists.infradead.org,
        Philipp Puschmann <philipp.puschmann@emlix.com>
Subject: [PATCH v3 1/3] dmaengine: imx-sdma: fix buffer ownership
Date:   Thu, 19 Sep 2019 12:45:24 +0200
Message-Id: <20190919104526.29851-2-philipp.puschmann@emlix.com>
In-Reply-To: <20190919104526.29851-1-philipp.puschmann@emlix.com>
References: <20190919102319.23368-1-philipp.puschmann@emlix.com>
 <20190919104526.29851-1-philipp.puschmann@emlix.com>
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BD_DONE flag marks ownership of the buffer. When 1 SDMA owns the
buffer, when 0 ARM owns it. When processing the buffers in
sdma_update_channel_loop the ownership of the currently processed
buffer was set to SDMA again before running the callback function of
the buffer and while the sdma script may be running in parallel. So
there was the possibility to get the buffer overwritten by SDMA before
it has been processed by kernel leading to kind of random errors in the
upper layers, e.g. bluetooth.

Fixes: broken since start
Signed-off-by: Philipp Puschmann <philipp.puschmann@emlix.com>

---

Changelog v3:
 - use correct dma_wmb() instead of dma_wb()
 - add fixes tag

Changelog v2:
 - add dma_wb()

 drivers/dma/imx-sdma.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
index 9ba74ab7e912..e029a2443cfc 100644
--- a/drivers/dma/imx-sdma.c
+++ b/drivers/dma/imx-sdma.c
@@ -802,7 +802,6 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
 		*/
 
 		desc->chn_real_count = bd->mode.count;
-		bd->mode.status |= BD_DONE;
 		bd->mode.count = desc->period_len;
 		desc->buf_ptail = desc->buf_tail;
 		desc->buf_tail = (desc->buf_tail + 1) % desc->num_bd;
@@ -817,6 +816,9 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
 		dmaengine_desc_get_callback_invoke(&desc->vd.tx, NULL);
 		spin_lock(&sdmac->vc.lock);
 
+		dma_wmb();
+		bd->mode.status |= BD_DONE;
+
 		if (error)
 			sdmac->status = old_status;
 	}
-- 
2.23.0