[PATCH 0/7] mmc: Several fixes for bcm2835 driver

[PATCH 0/7] mmc: Several fixes for bcm2835 driver

[Stefan Wahren]

This patch series fixes several issues which has been discovered after
submission.

Michal Suchanek (1):
  mmc: bcm2835: reset host on timeout

Phil Elwell (1):
  mmc: bcm2835: Recover from MMC_SEND_EXT_CSD

Stefan Wahren (5):
  mmc: bcm2835: Release DMA channel on driver unload
  mmc: bcm2835: Avoid possible races on data requests
  mmc: bcm2835: Terminate timeout work synchronously
  mmc: bcm2835: Refactor dma_map_sg handling
  mmc: bcm2835: Properly handle dmaengine_prep_slave_sg

 drivers/mmc/host/bcm2835.c | 58 ++++++++++++++++++++++++++++++----------------
 1 file changed, 38 insertions(+), 20 deletions(-)

-- 
2.7.4

[PATCH 0/7] mmc: Several fixes for bcm2835 driver

[Stefan Wahren]

This patch series fixes several issues which has been discovered after
submission.

Michal Suchanek (1):
  mmc: bcm2835: reset host on timeout

Phil Elwell (1):
  mmc: bcm2835: Recover from MMC_SEND_EXT_CSD

Stefan Wahren (5):
  mmc: bcm2835: Release DMA channel on driver unload
  mmc: bcm2835: Avoid possible races on data requests
  mmc: bcm2835: Terminate timeout work synchronously
  mmc: bcm2835: Refactor dma_map_sg handling
  mmc: bcm2835: Properly handle dmaengine_prep_slave_sg

 drivers/mmc/host/bcm2835.c | 58 ++++++++++++++++++++++++++++++----------------
 1 file changed, 38 insertions(+), 20 deletions(-)

-- 
2.7.4

[PATCH 1/7] mmc: bcm2835: reset host on timeout

[Stefan Wahren]

From: Michal Suchanek <msuchanek-l3A5Bk7waGM@public.gmane.org>

The bcm2835 mmc host tends to lock up for unknown reason so reset it on
timeout. The upper mmc block layer tries retransimitting with single
blocks which tends to work out after a long wait.

This is better than giving up and leaving the machine broken for no
obvious reason.

Fixes: 660fc733bd74 ("mmc: bcm2835: Add new driver for the sdhost controller.")
Signed-off-by: Michal Suchanek <msuchanek-l3A5Bk7waGM@public.gmane.org>
---
 drivers/mmc/host/bcm2835.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 768972a..f1712df 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -286,6 +286,7 @@ static void bcm2835_reset(struct mmc_host *mmc)
 
 	if (host->dma_chan)
 		dmaengine_terminate_sync(host->dma_chan);
+	host->dma_chan = NULL;
 	bcm2835_reset_internal(host);
 }
 
@@ -837,6 +838,8 @@ static void bcm2835_timeout(struct work_struct *work)
 		dev_err(dev, "timeout waiting for hardware interrupt.\n");
 		bcm2835_dumpregs(host);
 
+		bcm2835_reset(host->mmc);
+
 		if (host->data) {
 			host->data->error = -ETIMEDOUT;
 			bcm2835_finish_data(host);
-- 
2.7.4

[PATCH 1/7] mmc: bcm2835: reset host on timeout

[Stefan Wahren]

From: Michal Suchanek <msuchanek@suse.de>

The bcm2835 mmc host tends to lock up for unknown reason so reset it on
timeout. The upper mmc block layer tries retransimitting with single
blocks which tends to work out after a long wait.

This is better than giving up and leaving the machine broken for no
obvious reason.

Fixes: 660fc733bd74 ("mmc: bcm2835: Add new driver for the sdhost controller.")
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
---
 drivers/mmc/host/bcm2835.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 768972a..f1712df 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -286,6 +286,7 @@ static void bcm2835_reset(struct mmc_host *mmc)
 
 	if (host->dma_chan)
 		dmaengine_terminate_sync(host->dma_chan);
+	host->dma_chan = NULL;
 	bcm2835_reset_internal(host);
 }
 
@@ -837,6 +838,8 @@ static void bcm2835_timeout(struct work_struct *work)
 		dev_err(dev, "timeout waiting for hardware interrupt.\n");
 		bcm2835_dumpregs(host);
 
+		bcm2835_reset(host->mmc);
+
 		if (host->data) {
 			host->data->error = -ETIMEDOUT;
 			bcm2835_finish_data(host);
-- 
2.7.4

[PATCH 2/7] mmc: bcm2835: Recover from MMC_SEND_EXT_CSD

[Stefan Wahren]

From: Phil Elwell <phil@raspberrypi.org>

If the user issues an "mmc extcsd read", the SD controller receives
what it thinks is a SEND_IF_COND command with an unexpected data block.
The resulting operations leave the FSM stuck in READWAIT, a state which
persists until the MMC framework resets the controller, by which point
the root filesystem is likely to have been unmounted.

A less heavyweight solution is to detect the condition and nudge the
FSM by asserting the (self-clearing) FORCE_DATA_MODE bit.

Link: https://github.com/raspberrypi/linux/issues/2728
Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 drivers/mmc/host/bcm2835.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index f1712df..a251be2 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -773,6 +773,8 @@ static void bcm2835_finish_command(struct bcm2835_host *host)
 
 		if (!(sdhsts & SDHSTS_CRC7_ERROR) ||
 		    (host->cmd->opcode != MMC_SEND_OP_COND)) {
+			u32 edm, fsm;
+
 			if (sdhsts & SDHSTS_CMD_TIME_OUT) {
 				host->cmd->error = -ETIMEDOUT;
 			} else {
@@ -781,6 +783,13 @@ static void bcm2835_finish_command(struct bcm2835_host *host)
 				bcm2835_dumpregs(host);
 				host->cmd->error = -EILSEQ;
 			}
+			edm = readl(host->ioaddr + SDEDM);
+			fsm = edm & SDEDM_FSM_MASK;
+			if (fsm == SDEDM_FSM_READWAIT ||
+			    fsm == SDEDM_FSM_WRITESTART1)
+				/* Kick the FSM out of its wait */
+				writel(edm | SDEDM_FORCE_DATA_MODE,
+				       host->ioaddr + SDEDM);
 			bcm2835_finish_request(host);
 			return;
 		}
-- 
2.7.4

[PATCH 2/7] mmc: bcm2835: Recover from MMC_SEND_EXT_CSD

[Stefan Wahren]

From: Phil Elwell <phil@raspberrypi.org>

If the user issues an "mmc extcsd read", the SD controller receives
what it thinks is a SEND_IF_COND command with an unexpected data block.
The resulting operations leave the FSM stuck in READWAIT, a state which
persists until the MMC framework resets the controller, by which point
the root filesystem is likely to have been unmounted.

A less heavyweight solution is to detect the condition and nudge the
FSM by asserting the (self-clearing) FORCE_DATA_MODE bit.

Link: https://github.com/raspberrypi/linux/issues/2728
Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 drivers/mmc/host/bcm2835.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index f1712df..a251be2 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -773,6 +773,8 @@ static void bcm2835_finish_command(struct bcm2835_host *host)
 
 		if (!(sdhsts & SDHSTS_CRC7_ERROR) ||
 		    (host->cmd->opcode != MMC_SEND_OP_COND)) {
+			u32 edm, fsm;
+
 			if (sdhsts & SDHSTS_CMD_TIME_OUT) {
 				host->cmd->error = -ETIMEDOUT;
 			} else {
@@ -781,6 +783,13 @@ static void bcm2835_finish_command(struct bcm2835_host *host)
 				bcm2835_dumpregs(host);
 				host->cmd->error = -EILSEQ;
 			}
+			edm = readl(host->ioaddr + SDEDM);
+			fsm = edm & SDEDM_FSM_MASK;
+			if (fsm == SDEDM_FSM_READWAIT ||
+			    fsm == SDEDM_FSM_WRITESTART1)
+				/* Kick the FSM out of its wait */
+				writel(edm | SDEDM_FORCE_DATA_MODE,
+				       host->ioaddr + SDEDM);
 			bcm2835_finish_request(host);
 			return;
 		}
-- 
2.7.4

[PATCH 3/7] mmc: bcm2835: Release DMA channel on driver unload

[Stefan Wahren]

We need to release the slave DMA channel during driver unload.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index a251be2..45724ef 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -1457,6 +1457,9 @@ static int bcm2835_remove(struct platform_device *pdev)
 	cancel_work_sync(&host->dma_work);
 	cancel_delayed_work_sync(&host->timeout_work);
 
+	if (host->dma_chan_rxtx)
+		dma_release_channel(host->dma_chan_rxtx);
+
 	mmc_free_host(host->mmc);
 	platform_set_drvdata(pdev, NULL);
 
-- 
2.7.4

[PATCH 3/7] mmc: bcm2835: Release DMA channel on driver unload

[Stefan Wahren]

We need to release the slave DMA channel during driver unload.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index a251be2..45724ef 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -1457,6 +1457,9 @@ static int bcm2835_remove(struct platform_device *pdev)
 	cancel_work_sync(&host->dma_work);
 	cancel_delayed_work_sync(&host->timeout_work);
 
+	if (host->dma_chan_rxtx)
+		dma_release_channel(host->dma_chan_rxtx);
+
 	mmc_free_host(host->mmc);
 	platform_set_drvdata(pdev, NULL);
 
-- 
2.7.4

[PATCH 4/7] mmc: bcm2835: Avoid possible races on data requests

[Stefan Wahren]

There are two accesses on the data requests which are not protected by
the mutex. So fix this accordingly.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 45724ef..1c60798 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -1064,10 +1064,12 @@ static void bcm2835_dma_complete_work(struct work_struct *work)
 {
 	struct bcm2835_host *host =
 		container_of(work, struct bcm2835_host, dma_work);
-	struct mmc_data *data = host->data;
+	struct mmc_data *data;
 
 	mutex_lock(&host->mutex);
 
+	data = host->data;
+
 	if (host->dma_chan) {
 		dma_unmap_sg(host->dma_chan->device->dev,
 			     data->sg, data->sg_len,
@@ -1192,9 +1194,6 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
 		return;
 	}
 
-	if (host->use_dma && mrq->data && (mrq->data->blocks > PIO_THRESHOLD))
-		bcm2835_prepare_dma(host, mrq->data);
-
 	mutex_lock(&host->mutex);
 
 	WARN_ON(host->mrq);
@@ -1218,6 +1217,9 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
 		return;
 	}
 
+	if (host->use_dma && mrq->data && (mrq->data->blocks > PIO_THRESHOLD))
+		bcm2835_prepare_dma(host, mrq->data);
+
 	host->use_sbc = !!mrq->sbc && host->mrq->data &&
 			(host->mrq->data->flags & MMC_DATA_READ);
 	if (host->use_sbc) {
-- 
2.7.4

[PATCH 4/7] mmc: bcm2835: Avoid possible races on data requests

[Stefan Wahren]

There are two accesses on the data requests which are not protected by
the mutex. So fix this accordingly.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 45724ef..1c60798 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -1064,10 +1064,12 @@ static void bcm2835_dma_complete_work(struct work_struct *work)
 {
 	struct bcm2835_host *host =
 		container_of(work, struct bcm2835_host, dma_work);
-	struct mmc_data *data = host->data;
+	struct mmc_data *data;
 
 	mutex_lock(&host->mutex);
 
+	data = host->data;
+
 	if (host->dma_chan) {
 		dma_unmap_sg(host->dma_chan->device->dev,
 			     data->sg, data->sg_len,
@@ -1192,9 +1194,6 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
 		return;
 	}
 
-	if (host->use_dma && mrq->data && (mrq->data->blocks > PIO_THRESHOLD))
-		bcm2835_prepare_dma(host, mrq->data);
-
 	mutex_lock(&host->mutex);
 
 	WARN_ON(host->mrq);
@@ -1218,6 +1217,9 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
 		return;
 	}
 
+	if (host->use_dma && mrq->data && (mrq->data->blocks > PIO_THRESHOLD))
+		bcm2835_prepare_dma(host, mrq->data);
+
 	host->use_sbc = !!mrq->sbc && host->mrq->data &&
 			(host->mrq->data->flags & MMC_DATA_READ);
 	if (host->use_sbc) {
-- 
2.7.4

[PATCH 5/7] mmc: bcm2835: Terminate timeout work synchronously

[Stefan Wahren]

It's better to make sure that the timeout work is really terminated
before calling mmc_request_done.

Signed-off-by: Stefan Wahren <stefan.wahren-eS4NqCHxEME@public.gmane.org>
---
 drivers/mmc/host/bcm2835.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 1c60798..2c7589f 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -608,7 +608,7 @@ static void bcm2835_finish_request(struct bcm2835_host *host)
 	struct dma_chan *terminate_chan = NULL;
 	struct mmc_request *mrq;
 
-	cancel_delayed_work(&host->timeout_work);
+	cancel_delayed_work_sync(&host->timeout_work);
 
 	mrq = host->mrq;
 
-- 
2.7.4

[PATCH 5/7] mmc: bcm2835: Terminate timeout work synchronously

[Stefan Wahren]

It's better to make sure that the timeout work is really terminated
before calling mmc_request_done.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 1c60798..2c7589f 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -608,7 +608,7 @@ static void bcm2835_finish_request(struct bcm2835_host *host)
 	struct dma_chan *terminate_chan = NULL;
 	struct mmc_request *mrq;
 
-	cancel_delayed_work(&host->timeout_work);
+	cancel_delayed_work_sync(&host->timeout_work);
 
 	mrq = host->mrq;
 
-- 
2.7.4

[PATCH 6/7] mmc: bcm2835: Refactor dma_map_sg handling

[Stefan Wahren]

There are two variables len within bcm2835_prepare_dma. So rename the result
of dma_map_sg to sg_len. While we are at this add a bail out to simplify the
following change.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 2c7589f..c42bdaa 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -464,7 +464,7 @@ static void bcm2835_transfer_pio(struct bcm2835_host *host)
 static
 void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
 {
-	int len, dir_data, dir_slave;
+	int sg_len, dir_data, dir_slave;
 	struct dma_async_tx_descriptor *desc = NULL;
 	struct dma_chan *dma_chan;
 
@@ -510,15 +510,13 @@ void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
 				     &host->dma_cfg_rx :
 				     &host->dma_cfg_tx);
 
-	len = dma_map_sg(dma_chan->device->dev, data->sg, data->sg_len,
-			 dir_data);
+	sg_len = dma_map_sg(dma_chan->device->dev, data->sg, data->sg_len,
+			    dir_data);
+	if (!sg_len)
+		return;
 
-	if (len > 0) {
-		desc = dmaengine_prep_slave_sg(dma_chan, data->sg,
-					       len, dir_slave,
-					       DMA_PREP_INTERRUPT |
-					       DMA_CTRL_ACK);
-	}
+	desc = dmaengine_prep_slave_sg(dma_chan, data->sg, sg_len, dir_slave,
+				       DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 
 	if (desc) {
 		desc->callback = bcm2835_dma_complete;
-- 
2.7.4

[PATCH 6/7] mmc: bcm2835: Refactor dma_map_sg handling

[Stefan Wahren]

There are two variables len within bcm2835_prepare_dma. So rename the result
of dma_map_sg to sg_len. While we are at this add a bail out to simplify the
following change.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index 2c7589f..c42bdaa 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -464,7 +464,7 @@ static void bcm2835_transfer_pio(struct bcm2835_host *host)
 static
 void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
 {
-	int len, dir_data, dir_slave;
+	int sg_len, dir_data, dir_slave;
 	struct dma_async_tx_descriptor *desc = NULL;
 	struct dma_chan *dma_chan;
 
@@ -510,15 +510,13 @@ void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
 				     &host->dma_cfg_rx :
 				     &host->dma_cfg_tx);
 
-	len = dma_map_sg(dma_chan->device->dev, data->sg, data->sg_len,
-			 dir_data);
+	sg_len = dma_map_sg(dma_chan->device->dev, data->sg, data->sg_len,
+			    dir_data);
+	if (!sg_len)
+		return;
 
-	if (len > 0) {
-		desc = dmaengine_prep_slave_sg(dma_chan, data->sg,
-					       len, dir_slave,
-					       DMA_PREP_INTERRUPT |
-					       DMA_CTRL_ACK);
-	}
+	desc = dmaengine_prep_slave_sg(dma_chan, data->sg, sg_len, dir_slave,
+				       DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 
 	if (desc) {
 		desc->callback = bcm2835_dma_complete;
-- 
2.7.4

[PATCH 7/7] mmc: bcm2835: Properly handle dmaengine_prep_slave_sg

[Stefan Wahren]

In case dmaengine_prep_slave_sg fails we need to call dma_unmap_sg.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index c42bdaa..82e4b08 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -518,13 +518,16 @@ void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
 	desc = dmaengine_prep_slave_sg(dma_chan, data->sg, sg_len, dir_slave,
 				       DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 
-	if (desc) {
-		desc->callback = bcm2835_dma_complete;
-		desc->callback_param = host;
-		host->dma_desc = desc;
-		host->dma_chan = dma_chan;
-		host->dma_dir = dir_data;
+	if (!desc) {
+		dma_unmap_sg(dma_chan->device->dev, data->sg, sg_len, dir_data);
+		return;
 	}
+
+	desc->callback = bcm2835_dma_complete;
+	desc->callback_param = host;
+	host->dma_desc = desc;
+	host->dma_chan = dma_chan;
+	host->dma_dir = dir_data;
 }
 
 static void bcm2835_start_dma(struct bcm2835_host *host)
-- 
2.7.4

[PATCH 7/7] mmc: bcm2835: Properly handle dmaengine_prep_slave_sg

[Stefan Wahren]

In case dmaengine_prep_slave_sg fails we need to call dma_unmap_sg.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 drivers/mmc/host/bcm2835.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/mmc/host/bcm2835.c b/drivers/mmc/host/bcm2835.c
index c42bdaa..82e4b08 100644
--- a/drivers/mmc/host/bcm2835.c
+++ b/drivers/mmc/host/bcm2835.c
@@ -518,13 +518,16 @@ void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
 	desc = dmaengine_prep_slave_sg(dma_chan, data->sg, sg_len, dir_slave,
 				       DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 
-	if (desc) {
-		desc->callback = bcm2835_dma_complete;
-		desc->callback_param = host;
-		host->dma_desc = desc;
-		host->dma_chan = dma_chan;
-		host->dma_dir = dir_data;
+	if (!desc) {
+		dma_unmap_sg(dma_chan->device->dev, data->sg, sg_len, dir_data);
+		return;
 	}
+
+	desc->callback = bcm2835_dma_complete;
+	desc->callback_param = host;
+	host->dma_desc = desc;
+	host->dma_chan = dma_chan;
+	host->dma_dir = dir_data;
 }
 
 static void bcm2835_start_dma(struct bcm2835_host *host)
-- 
2.7.4