[PATCH v6 0/3] dmaengine: xilinx_dma: Bug fixes

[PATCH v6 0/3] dmaengine: xilinx_dma: Bug fixes

[Kedareswara rao Appana]

This patch series fixes below bugs in DMA and VDMA IP's
---> Do not start VDMA until frame buffer is processed by the h/w
---> Fix bug in Multi frame sotres handling in VDMA
---> Fix issues w.r.to multi frame descriptors submit with AXI DMA S2MM(recv) Side.

Kedareswara rao Appana (3):
  dmaengine: xilinx_dma: Check for channel idle state before submitting
    dma descriptor
  dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in
    vdma
  dmaengine: xilinx_dma: Fix race condition in the driver for multiple
    descriptor scenario

 .../devicetree/bindings/dma/xilinx/xilinx_dma.txt  |   2 +
 drivers/dma/xilinx/xilinx_dma.c                    | 270 ++++++++++++---------
 2 files changed, 161 insertions(+), 111 deletions(-)

-- 
2.1.2

[PATCH v6 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

[Kedareswara rao Appana]

Add variable for checking channel idle state to ensure that dma descriptor is not
Submitted when DMA engine is in progress.

This will avoids the pollling for a bit in the status register to know
Dma state in the driver hot path.

Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
---
Changes for v6:
---> Updated commit message as suggested by Vinod.
---> Added Channel idle variable description in the driver
     as suggested by Vinod.
Changes for v5:
---> None.
Changes for v4:
---> None.
Changes for v3:
---> None.
Changes for v2:
---> Add idle check in the reset as suggested by Jose Abreu
---> Removed xilinx_dma_is_running/xilinx_dma_is_idle checks
    in the driver and used common idle checks across the driver
    as suggested by Laurent Pinchart.

 drivers/dma/xilinx/xilinx_dma.c | 61 +++++++++++++++--------------------------
 1 file changed, 22 insertions(+), 39 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 8288fe4..5eeea57 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -321,6 +321,7 @@ struct xilinx_dma_tx_descriptor {
  * @cyclic: Check for cyclic transfers.
  * @genlock: Support genlock mode
  * @err: Channel has errors
+ * @idle: Check for channel idle
  * @tasklet: Cleanup work after irq
  * @config: Device configuration info
  * @flush_on_fsync: Flush on Frame sync
@@ -351,6 +352,7 @@ struct xilinx_dma_chan {
 	bool cyclic;
 	bool genlock;
 	bool err;
+	bool idle;
 	struct tasklet_struct tasklet;
 	struct xilinx_vdma_config config;
 	bool flush_on_fsync;
@@ -920,32 +922,6 @@ static enum dma_status xilinx_dma_tx_status(struct dma_chan *dchan,
 }
 
 /**
- * xilinx_dma_is_running - Check if DMA channel is running
- * @chan: Driver specific DMA channel
- *
- * Return: '1' if running, '0' if not.
- */
-static bool xilinx_dma_is_running(struct xilinx_dma_chan *chan)
-{
-	return !(dma_ctrl_read(chan, XILINX_DMA_REG_DMASR) &
-		 XILINX_DMA_DMASR_HALTED) &&
-		(dma_ctrl_read(chan, XILINX_DMA_REG_DMACR) &
-		 XILINX_DMA_DMACR_RUNSTOP);
-}
-
-/**
- * xilinx_dma_is_idle - Check if DMA channel is idle
- * @chan: Driver specific DMA channel
- *
- * Return: '1' if idle, '0' if not.
- */
-static bool xilinx_dma_is_idle(struct xilinx_dma_chan *chan)
-{
-	return dma_ctrl_read(chan, XILINX_DMA_REG_DMASR) &
-		XILINX_DMA_DMASR_IDLE;
-}
-
-/**
  * xilinx_dma_halt - Halt DMA channel
  * @chan: Driver specific DMA channel
  */
@@ -966,6 +942,7 @@ static void xilinx_dma_halt(struct xilinx_dma_chan *chan)
 			chan, dma_ctrl_read(chan, XILINX_DMA_REG_DMASR));
 		chan->err = true;
 	}
+	chan->idle = true;
 }
 
 /**
@@ -1007,6 +984,9 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
 	if (chan->err)
 		return;
 
+	if (!chan->idle)
+		return;
+
 	if (list_empty(&chan->pending_list))
 		return;
 
@@ -1018,13 +998,6 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
 	tail_segment = list_last_entry(&tail_desc->segments,
 				       struct xilinx_vdma_tx_segment, node);
 
-	/* If it is SG mode and hardware is busy, cannot submit */
-	if (chan->has_sg && xilinx_dma_is_running(chan) &&
-	    !xilinx_dma_is_idle(chan)) {
-		dev_dbg(chan->dev, "DMA controller still busy\n");
-		return;
-	}
-
 	/*
 	 * If hardware is idle, then all descriptors on the running lists are
 	 * done, start new transfers
@@ -1110,6 +1083,7 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
 		vdma_desc_write(chan, XILINX_DMA_REG_VSIZE, last->hw.vsize);
 	}
 
+	chan->idle = false;
 	if (!chan->has_sg) {
 		list_del(&desc->node);
 		list_add_tail(&desc->node, &chan->active_list);
@@ -1136,6 +1110,9 @@ static void xilinx_cdma_start_transfer(struct xilinx_dma_chan *chan)
 	if (chan->err)
 		return;
 
+	if (!chan->idle)
+		return;
+
 	if (list_empty(&chan->pending_list))
 		return;
 
@@ -1181,6 +1158,7 @@ static void xilinx_cdma_start_transfer(struct xilinx_dma_chan *chan)
 
 	list_splice_tail_init(&chan->pending_list, &chan->active_list);
 	chan->desc_pendingcount = 0;
+	chan->idle = false;
 }
 
 /**
@@ -1196,15 +1174,11 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 	if (chan->err)
 		return;
 
-	if (list_empty(&chan->pending_list))
+	if (!chan->idle)
 		return;
 
-	/* If it is SG mode and hardware is busy, cannot submit */
-	if (chan->has_sg && xilinx_dma_is_running(chan) &&
-	    !xilinx_dma_is_idle(chan)) {
-		dev_dbg(chan->dev, "DMA controller still busy\n");
+	if (list_empty(&chan->pending_list))
 		return;
-	}
 
 	head_desc = list_first_entry(&chan->pending_list,
 				     struct xilinx_dma_tx_descriptor, node);
@@ -1302,6 +1276,7 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 
 	list_splice_tail_init(&chan->pending_list, &chan->active_list);
 	chan->desc_pendingcount = 0;
+	chan->idle = false;
 }
 
 /**
@@ -1366,6 +1341,7 @@ static int xilinx_dma_reset(struct xilinx_dma_chan *chan)
 	}
 
 	chan->err = false;
+	chan->idle = true;
 
 	return err;
 }
@@ -1447,6 +1423,7 @@ static irqreturn_t xilinx_dma_irq_handler(int irq, void *data)
 	if (status & XILINX_DMA_DMASR_FRM_CNT_IRQ) {
 		spin_lock(&chan->lock);
 		xilinx_dma_complete_descriptor(chan);
+		chan->idle = true;
 		chan->start_transfer(chan);
 		spin_unlock(&chan->lock);
 	}
@@ -2327,6 +2304,12 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
 	chan->has_sg = xdev->has_sg;
 	chan->desc_pendingcount = 0x0;
 	chan->ext_addr = xdev->ext_addr;
+	/* This variable enusres that descripotrs are not
+	 * Submited when dma engine is in progress. This variable is
+	 * Added to avoid pollling for a bit in the status register to
+	 * Know dma state in the driver hot path.
+	 */
+	chan->idle = true;
 
 	spin_lock_init(&chan->lock);
 	INIT_LIST_HEAD(&chan->pending_list);
-- 
2.1.2

[PATCH v6 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

[Kedareswara rao Appana]

When VDMA is configured for more than one frame in the h/w.
For example h/w is configured for n number of frames, user
Submits n number of frames and triggered the DMA using issue_pending API.

In the current driver flow we are submitting one frame at a time,
But we should submit all the n number of frames at one time
As the h/w is configured for n number of frames.

This patch fixes this issue.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
---
Changes for v6:
---> Added Rob Acked-by
---> Updated commit message as suggested by Vinod.
Changes for v5:
---> Updated xlnx,fstore-config property to xlnx,fstore-enable
     and updated description as suggested by Rob.
Changes for v4:
---> Add Check for framestore configuration on Transmit case as well
     as suggested by Jose Abreu.
---> Modified the dev_dbg checks to dev_warn checks as suggested
     by Jose Abreu.
Changes for v3:
---> Added Checks for frame store configuration. If frame store
     Configuration is not present at the h/w level and user
     Submits less frames added debug prints in the driver as relevant.
Changes for v2:
---> Fixed race conditions in the driver as suggested by Jose Abreu
---> Fixed unnecessray if else checks in the vdma_start_transfer
     as suggested by Laurent Pinchart.

 .../devicetree/bindings/dma/xilinx/xilinx_dma.txt  |  2 +
 drivers/dma/xilinx/xilinx_dma.c                    | 78 +++++++++++++++-------
 2 files changed, 57 insertions(+), 23 deletions(-)

diff --git a/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt b/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
index a2b8bfa..e951c09 100644
--- a/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
+++ b/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
@@ -66,6 +66,8 @@ Optional child node properties:
 Optional child node properties for VDMA:
 - xlnx,genlock-mode: Tells Genlock synchronization is
 	enabled/disabled in hardware.
+- xlnx,fstore-enable: boolean; if defined, it indicates that controller
+	supports frame store configuration.
 Optional child node properties for AXI DMA:
 -dma-channels: Number of dma channels in child node.
 
diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 5eeea57..edb5b71 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -322,6 +322,7 @@ struct xilinx_dma_tx_descriptor {
  * @genlock: Support genlock mode
  * @err: Channel has errors
  * @idle: Check for channel idle
+ * @has_fstoreen: Check for frame store configuration
  * @tasklet: Cleanup work after irq
  * @config: Device configuration info
  * @flush_on_fsync: Flush on Frame sync
@@ -353,6 +354,7 @@ struct xilinx_dma_chan {
 	bool genlock;
 	bool err;
 	bool idle;
+	bool has_fstoreen;
 	struct tasklet_struct tasklet;
 	struct xilinx_vdma_config config;
 	bool flush_on_fsync;
@@ -990,6 +992,27 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
 	if (list_empty(&chan->pending_list))
 		return;
 
+	/*
+	 * Note: When VDMA is built with default h/w configuration
+	 * User should submit frames upto H/W configured.
+	 * If users submits less than h/w configured
+	 * VDMA engine tries to write to a invalid location
+	 * Results undefined behaviour/memory corruption.
+	 *
+	 * If user would like to submit frames less than h/w capable
+	 * On S2MM side please enable debug info 13 at the h/w level
+	 * On MM2S side please enable debug info 6 at the h/w level
+	 * It will allows the frame buffers numbers to be modified at runtime.
+	 */
+	if (!chan->has_fstoreen &&
+	     chan->desc_pendingcount < chan->num_frms) {
+		dev_warn(chan->dev, "Frame Store Configuration is not enabled at the\n");
+		dev_warn(chan->dev, "H/w level enable Debug info 13 or 6 at the h/w level\n");
+		dev_warn(chan->dev, "OR Submit the frames upto h/w Capable\n\r");
+
+		return;
+	}
+
 	desc = list_first_entry(&chan->pending_list,
 				struct xilinx_dma_tx_descriptor, node);
 	tail_desc = list_last_entry(&chan->pending_list,
@@ -1052,25 +1075,38 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
 	if (chan->has_sg) {
 		dma_ctrl_write(chan, XILINX_DMA_REG_TAILDESC,
 				tail_segment->phys);
+		list_splice_tail_init(&chan->pending_list, &chan->active_list);
+		chan->desc_pendingcount = 0;
 	} else {
 		struct xilinx_vdma_tx_segment *segment, *last = NULL;
-		int i = 0;
+		int i = 0, j = 0;
 
 		if (chan->desc_submitcount < chan->num_frms)
 			i = chan->desc_submitcount;
 
-		list_for_each_entry(segment, &desc->segments, node) {
-			if (chan->ext_addr)
-				vdma_desc_write_64(chan,
-					XILINX_VDMA_REG_START_ADDRESS_64(i++),
-					segment->hw.buf_addr,
-					segment->hw.buf_addr_msb);
-			else
-				vdma_desc_write(chan,
-					XILINX_VDMA_REG_START_ADDRESS(i++),
-					segment->hw.buf_addr);
-
-			last = segment;
+		for (j = 0; j < chan->num_frms; ) {
+			list_for_each_entry(segment, &desc->segments, node) {
+				if (chan->ext_addr)
+					vdma_desc_write_64(chan,
+					  XILINX_VDMA_REG_START_ADDRESS_64(i++),
+					  segment->hw.buf_addr,
+					  segment->hw.buf_addr_msb);
+				else
+					vdma_desc_write(chan,
+					    XILINX_VDMA_REG_START_ADDRESS(i++),
+					    segment->hw.buf_addr);
+
+				last = segment;
+			}
+			list_del(&desc->node);
+			list_add_tail(&desc->node, &chan->active_list);
+			j++;
+			if (list_empty(&chan->pending_list) ||
+			    (i == chan->num_frms))
+				break;
+			desc = list_first_entry(&chan->pending_list,
+						struct xilinx_dma_tx_descriptor,
+						node);
 		}
 
 		if (!last)
@@ -1081,20 +1117,14 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
 		vdma_desc_write(chan, XILINX_DMA_REG_FRMDLY_STRIDE,
 				last->hw.stride);
 		vdma_desc_write(chan, XILINX_DMA_REG_VSIZE, last->hw.vsize);
-	}
 
-	chan->idle = false;
-	if (!chan->has_sg) {
-		list_del(&desc->node);
-		list_add_tail(&desc->node, &chan->active_list);
-		chan->desc_submitcount++;
-		chan->desc_pendingcount--;
+		chan->desc_submitcount += j;
+		chan->desc_pendingcount -= j;
 		if (chan->desc_submitcount == chan->num_frms)
 			chan->desc_submitcount = 0;
-	} else {
-		list_splice_tail_init(&chan->pending_list, &chan->active_list);
-		chan->desc_pendingcount = 0;
 	}
+
+	chan->idle = false;
 }
 
 /**
@@ -1342,6 +1372,7 @@ static int xilinx_dma_reset(struct xilinx_dma_chan *chan)
 
 	chan->err = false;
 	chan->idle = true;
+	chan->desc_submitcount = 0;
 
 	return err;
 }
@@ -2320,6 +2351,7 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
 	has_dre = of_property_read_bool(node, "xlnx,include-dre");
 
 	chan->genlock = of_property_read_bool(node, "xlnx,genlock-mode");
+	chan->has_fstoreen = of_property_read_bool(node, "xlnx,fstore-enable");
 
 	err = of_property_read_u32(node, "xlnx,datawidth", &value);
 	if (err) {
-- 
2.1.2

[PATCH v6 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

[Mike Looijmans]

?On 14-01-17 06:35, Kedareswara rao Appana wrote:
> When VDMA is configured for more than one frame in the h/w.
> For example h/w is configured for n number of frames, user
> Submits n number of frames and triggered the DMA using issue_pending API.
>
> In the current driver flow we are submitting one frame at a time,
> But we should submit all the n number of frames at one time
> As the h/w is configured for n number of frames.

The hardware can always handle a single frame submission, by using the "park" 
bit. This would make a good "cyclic" implementation too (using vdma as 
framebuffer).

It could also handle all cases for "k" frames where n%k==0 (n is a multiple of 
k) by simply replicating the frame pointers.

>
> This patch fixes this issue.
>
> Acked-by: Rob Herring <robh@kernel.org>
> Reviewed-by: Jose Abreu <joabreu@synopsys.com>
> Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> ---
> Changes for v6:
> ---> Added Rob Acked-by
> ---> Updated commit message as suggested by Vinod.
> Changes for v5:
> ---> Updated xlnx,fstore-config property to xlnx,fstore-enable
>      and updated description as suggested by Rob.
> Changes for v4:
> ---> Add Check for framestore configuration on Transmit case as well
>      as suggested by Jose Abreu.
> ---> Modified the dev_dbg checks to dev_warn checks as suggested
>      by Jose Abreu.
> Changes for v3:
> ---> Added Checks for frame store configuration. If frame store
>      Configuration is not present at the h/w level and user
>      Submits less frames added debug prints in the driver as relevant.
> Changes for v2:
> ---> Fixed race conditions in the driver as suggested by Jose Abreu
> ---> Fixed unnecessray if else checks in the vdma_start_transfer
>      as suggested by Laurent Pinchart.
>
>  .../devicetree/bindings/dma/xilinx/xilinx_dma.txt  |  2 +
>  drivers/dma/xilinx/xilinx_dma.c                    | 78 +++++++++++++++-------
>  2 files changed, 57 insertions(+), 23 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt b/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
> index a2b8bfa..e951c09 100644
> --- a/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
> +++ b/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
> @@ -66,6 +66,8 @@ Optional child node properties:
>  Optional child node properties for VDMA:
>  - xlnx,genlock-mode: Tells Genlock synchronization is
>  	enabled/disabled in hardware.
> +- xlnx,fstore-enable: boolean; if defined, it indicates that controller
> +	supports frame store configuration.
>  Optional child node properties for AXI DMA:
>  -dma-channels: Number of dma channels in child node.
>
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index 5eeea57..edb5b71 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -322,6 +322,7 @@ struct xilinx_dma_tx_descriptor {
>   * @genlock: Support genlock mode
>   * @err: Channel has errors
>   * @idle: Check for channel idle
> + * @has_fstoreen: Check for frame store configuration
>   * @tasklet: Cleanup work after irq
>   * @config: Device configuration info
>   * @flush_on_fsync: Flush on Frame sync
> @@ -353,6 +354,7 @@ struct xilinx_dma_chan {
>  	bool genlock;
>  	bool err;
>  	bool idle;
> +	bool has_fstoreen;
>  	struct tasklet_struct tasklet;
>  	struct xilinx_vdma_config config;
>  	bool flush_on_fsync;
> @@ -990,6 +992,27 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
>  	if (list_empty(&chan->pending_list))
>  		return;
>
> +	/*
> +	 * Note: When VDMA is built with default h/w configuration
> +	 * User should submit frames upto H/W configured.
> +	 * If users submits less than h/w configured
> +	 * VDMA engine tries to write to a invalid location
> +	 * Results undefined behaviour/memory corruption.
> +	 *
> +	 * If user would like to submit frames less than h/w capable
> +	 * On S2MM side please enable debug info 13 at the h/w level
> +	 * On MM2S side please enable debug info 6 at the h/w level
> +	 * It will allows the frame buffers numbers to be modified at runtime.
> +	 */
> +	if (!chan->has_fstoreen &&
> +	     chan->desc_pendingcount < chan->num_frms) {
> +		dev_warn(chan->dev, "Frame Store Configuration is not enabled at the\n");
> +		dev_warn(chan->dev, "H/w level enable Debug info 13 or 6 at the h/w level\n");
> +		dev_warn(chan->dev, "OR Submit the frames upto h/w Capable\n\r");
> +
> +		return;
> +	}
> +
>  	desc = list_first_entry(&chan->pending_list,
>  				struct xilinx_dma_tx_descriptor, node);
>  	tail_desc = list_last_entry(&chan->pending_list,
> @@ -1052,25 +1075,38 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
>  	if (chan->has_sg) {
>  		dma_ctrl_write(chan, XILINX_DMA_REG_TAILDESC,
>  				tail_segment->phys);
> +		list_splice_tail_init(&chan->pending_list, &chan->active_list);
> +		chan->desc_pendingcount = 0;
>  	} else {
>  		struct xilinx_vdma_tx_segment *segment, *last = NULL;
> -		int i = 0;
> +		int i = 0, j = 0;
>
>  		if (chan->desc_submitcount < chan->num_frms)
>  			i = chan->desc_submitcount;
>
> -		list_for_each_entry(segment, &desc->segments, node) {
> -			if (chan->ext_addr)
> -				vdma_desc_write_64(chan,
> -					XILINX_VDMA_REG_START_ADDRESS_64(i++),
> -					segment->hw.buf_addr,
> -					segment->hw.buf_addr_msb);
> -			else
> -				vdma_desc_write(chan,
> -					XILINX_VDMA_REG_START_ADDRESS(i++),
> -					segment->hw.buf_addr);
> -
> -			last = segment;
> +		for (j = 0; j < chan->num_frms; ) {
> +			list_for_each_entry(segment, &desc->segments, node) {
> +				if (chan->ext_addr)
> +					vdma_desc_write_64(chan,
> +					  XILINX_VDMA_REG_START_ADDRESS_64(i++),
> +					  segment->hw.buf_addr,
> +					  segment->hw.buf_addr_msb);
> +				else
> +					vdma_desc_write(chan,
> +					    XILINX_VDMA_REG_START_ADDRESS(i++),
> +					    segment->hw.buf_addr);
> +
> +				last = segment;
> +			}
> +			list_del(&desc->node);
> +			list_add_tail(&desc->node, &chan->active_list);
> +			j++;
> +			if (list_empty(&chan->pending_list) ||
> +			    (i == chan->num_frms))
> +				break;
> +			desc = list_first_entry(&chan->pending_list,
> +						struct xilinx_dma_tx_descriptor,
> +						node);
>  		}
>
>  		if (!last)
> @@ -1081,20 +1117,14 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
>  		vdma_desc_write(chan, XILINX_DMA_REG_FRMDLY_STRIDE,
>  				last->hw.stride);
>  		vdma_desc_write(chan, XILINX_DMA_REG_VSIZE, last->hw.vsize);
> -	}
>
> -	chan->idle = false;
> -	if (!chan->has_sg) {
> -		list_del(&desc->node);
> -		list_add_tail(&desc->node, &chan->active_list);
> -		chan->desc_submitcount++;
> -		chan->desc_pendingcount--;
> +		chan->desc_submitcount += j;
> +		chan->desc_pendingcount -= j;
>  		if (chan->desc_submitcount == chan->num_frms)
>  			chan->desc_submitcount = 0;
> -	} else {
> -		list_splice_tail_init(&chan->pending_list, &chan->active_list);
> -		chan->desc_pendingcount = 0;
>  	}
> +
> +	chan->idle = false;
>  }
>
>  /**
> @@ -1342,6 +1372,7 @@ static int xilinx_dma_reset(struct xilinx_dma_chan *chan)
>
>  	chan->err = false;
>  	chan->idle = true;
> +	chan->desc_submitcount = 0;
>
>  	return err;
>  }
> @@ -2320,6 +2351,7 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
>  	has_dre = of_property_read_bool(node, "xlnx,include-dre");
>
>  	chan->genlock = of_property_read_bool(node, "xlnx,genlock-mode");
> +	chan->has_fstoreen = of_property_read_bool(node, "xlnx,fstore-enable");
>
>  	err = of_property_read_u32(node, "xlnx,datawidth", &value);
>  	if (err) {
>



Kind regards,

Mike Looijmans
System Expert

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[PATCH v6 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

[Appana Durga Kedareswara Rao]

Hi Mike Looijmans,

	Thanks for the review...
	Sorry for the long delay in the reply...
Please find comments inline... 

<Snip>
>On 14-01-17 06:35, Kedareswara rao Appana wrote:
>>??When VDMA is configured for more than one frame in the h/w.
>>??For example h/w is configured for n number of frames, user
>>??Submits n number of frames and triggered the DMA using issue_pending API.
>>
>>??In the current driver flow we are submitting one frame at a time,
>>??But we should submit all the n number of frames at one time
>>??As the h/w is configured for n number of frames.
>
>The hardware can always handle a single frame submission, by using the "park"
>bit. This would make a good "cyclic" implementation too (using vdma as
>framebuffer).
>
>It could also handle all cases for "k" frames where n%k==0 (n is a multiple of
>k) by simply replicating the frame pointers.

Agree with your comments will fix it in the next version.
Somehow didn't get enough time to send next version of the patch series.
Will modify the driver as per your comments and will post next version of the patch series at the earliest... 

Regards,
Kedar.

[PATCH v6 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

[Vinod Koul]

On Sat, Jan 14, 2017 at 11:05:54AM +0530, Kedareswara rao Appana wrote:
> When VDMA is configured for more than one frame in the h/w.
> For example h/w is configured for n number of frames, user
> Submits n number of frames and triggered the DMA using issue_pending API.
> 
> In the current driver flow we are submitting one frame at a time,
> But we should submit all the n number of frames at one time
> As the h/w is configured for n number of frames.

Is there a specific reason why you continue to start lines with Title cases, I
have already told you to not do that last time!

> 
> This patch fixes this issue.
> 
> Acked-by: Rob Herring <robh@kernel.org>
> Reviewed-by: Jose Abreu <joabreu@synopsys.com>
> Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> ---
> Changes for v6:
> ---> Added Rob Acked-by
> ---> Updated commit message as suggested by Vinod.
> Changes for v5:
> ---> Updated xlnx,fstore-config property to xlnx,fstore-enable
>      and updated description as suggested by Rob.
> Changes for v4:
> ---> Add Check for framestore configuration on Transmit case as well
>      as suggested by Jose Abreu.
> ---> Modified the dev_dbg checks to dev_warn checks as suggested
>      by Jose Abreu.
> Changes for v3:
> ---> Added Checks for frame store configuration. If frame store
>      Configuration is not present at the h/w level and user
>      Submits less frames added debug prints in the driver as relevant.
> Changes for v2:
> ---> Fixed race conditions in the driver as suggested by Jose Abreu
> ---> Fixed unnecessray if else checks in the vdma_start_transfer
>      as suggested by Laurent Pinchart.
> 
>  .../devicetree/bindings/dma/xilinx/xilinx_dma.txt  |  2 +
>  drivers/dma/xilinx/xilinx_dma.c                    | 78 +++++++++++++++-------
>  2 files changed, 57 insertions(+), 23 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt b/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
> index a2b8bfa..e951c09 100644
> --- a/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
> +++ b/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt
> @@ -66,6 +66,8 @@ Optional child node properties:
>  Optional child node properties for VDMA:
>  - xlnx,genlock-mode: Tells Genlock synchronization is
>  	enabled/disabled in hardware.
> +- xlnx,fstore-enable: boolean; if defined, it indicates that controller
> +	supports frame store configuration.
>  Optional child node properties for AXI DMA:
>  -dma-channels: Number of dma channels in child node.
>  
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index 5eeea57..edb5b71 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -322,6 +322,7 @@ struct xilinx_dma_tx_descriptor {
>   * @genlock: Support genlock mode
>   * @err: Channel has errors
>   * @idle: Check for channel idle
> + * @has_fstoreen: Check for frame store configuration
>   * @tasklet: Cleanup work after irq
>   * @config: Device configuration info
>   * @flush_on_fsync: Flush on Frame sync
> @@ -353,6 +354,7 @@ struct xilinx_dma_chan {
>  	bool genlock;
>  	bool err;
>  	bool idle;
> +	bool has_fstoreen;
>  	struct tasklet_struct tasklet;
>  	struct xilinx_vdma_config config;
>  	bool flush_on_fsync;
> @@ -990,6 +992,27 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
>  	if (list_empty(&chan->pending_list))
>  		return;
>  
> +	/*
> +	 * Note: When VDMA is built with default h/w configuration
> +	 * User should submit frames upto H/W configured.
> +	 * If users submits less than h/w configured
> +	 * VDMA engine tries to write to a invalid location
> +	 * Results undefined behaviour/memory corruption.
> +	 *
> +	 * If user would like to submit frames less than h/w capable
> +	 * On S2MM side please enable debug info 13 at the h/w level
> +	 * On MM2S side please enable debug info 6 at the h/w level
> +	 * It will allows the frame buffers numbers to be modified at runtime.
> +	 */
> +	if (!chan->has_fstoreen &&
> +	     chan->desc_pendingcount < chan->num_frms) {
> +		dev_warn(chan->dev, "Frame Store Configuration is not enabled at the\n");
> +		dev_warn(chan->dev, "H/w level enable Debug info 13 or 6 at the h/w level\n");
> +		dev_warn(chan->dev, "OR Submit the frames upto h/w Capable\n\r");
> +
> +		return;
> +	}
> +
>  	desc = list_first_entry(&chan->pending_list,
>  				struct xilinx_dma_tx_descriptor, node);
>  	tail_desc = list_last_entry(&chan->pending_list,
> @@ -1052,25 +1075,38 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
>  	if (chan->has_sg) {
>  		dma_ctrl_write(chan, XILINX_DMA_REG_TAILDESC,
>  				tail_segment->phys);
> +		list_splice_tail_init(&chan->pending_list, &chan->active_list);
> +		chan->desc_pendingcount = 0;
>  	} else {
>  		struct xilinx_vdma_tx_segment *segment, *last = NULL;
> -		int i = 0;
> +		int i = 0, j = 0;
>  
>  		if (chan->desc_submitcount < chan->num_frms)
>  			i = chan->desc_submitcount;
>  
> -		list_for_each_entry(segment, &desc->segments, node) {
> -			if (chan->ext_addr)
> -				vdma_desc_write_64(chan,
> -					XILINX_VDMA_REG_START_ADDRESS_64(i++),
> -					segment->hw.buf_addr,
> -					segment->hw.buf_addr_msb);
> -			else
> -				vdma_desc_write(chan,
> -					XILINX_VDMA_REG_START_ADDRESS(i++),
> -					segment->hw.buf_addr);
> -
> -			last = segment;
> +		for (j = 0; j < chan->num_frms; ) {
> +			list_for_each_entry(segment, &desc->segments, node) {
> +				if (chan->ext_addr)
> +					vdma_desc_write_64(chan,
> +					  XILINX_VDMA_REG_START_ADDRESS_64(i++),
> +					  segment->hw.buf_addr,
> +					  segment->hw.buf_addr_msb);
> +				else
> +					vdma_desc_write(chan,
> +					    XILINX_VDMA_REG_START_ADDRESS(i++),
> +					    segment->hw.buf_addr);
> +
> +				last = segment;
> +			}
> +			list_del(&desc->node);
> +			list_add_tail(&desc->node, &chan->active_list);
> +			j++;
> +			if (list_empty(&chan->pending_list) ||
> +			    (i == chan->num_frms))
> +				break;
> +			desc = list_first_entry(&chan->pending_list,
> +						struct xilinx_dma_tx_descriptor,
> +						node);
>  		}
>  
>  		if (!last)
> @@ -1081,20 +1117,14 @@ static void xilinx_vdma_start_transfer(struct xilinx_dma_chan *chan)
>  		vdma_desc_write(chan, XILINX_DMA_REG_FRMDLY_STRIDE,
>  				last->hw.stride);
>  		vdma_desc_write(chan, XILINX_DMA_REG_VSIZE, last->hw.vsize);
> -	}
>  
> -	chan->idle = false;
> -	if (!chan->has_sg) {
> -		list_del(&desc->node);
> -		list_add_tail(&desc->node, &chan->active_list);
> -		chan->desc_submitcount++;
> -		chan->desc_pendingcount--;
> +		chan->desc_submitcount += j;
> +		chan->desc_pendingcount -= j;
>  		if (chan->desc_submitcount == chan->num_frms)
>  			chan->desc_submitcount = 0;
> -	} else {
> -		list_splice_tail_init(&chan->pending_list, &chan->active_list);
> -		chan->desc_pendingcount = 0;
>  	}
> +
> +	chan->idle = false;
>  }
>  
>  /**
> @@ -1342,6 +1372,7 @@ static int xilinx_dma_reset(struct xilinx_dma_chan *chan)
>  
>  	chan->err = false;
>  	chan->idle = true;
> +	chan->desc_submitcount = 0;
>  
>  	return err;
>  }
> @@ -2320,6 +2351,7 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
>  	has_dre = of_property_read_bool(node, "xlnx,include-dre");
>  
>  	chan->genlock = of_property_read_bool(node, "xlnx,genlock-mode");
> +	chan->has_fstoreen = of_property_read_bool(node, "xlnx,fstore-enable");
>  
>  	err = of_property_read_u32(node, "xlnx,datawidth", &value);
>  	if (err) {
> -- 
> 2.1.2
> 

-- 
~Vinod

[PATCH v6 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Kedareswara rao Appana]

As per AXI DMA spec the software must not move the tail pointer to a location
That has not been updated (next descriptor field of the h/w descriptor
Should always point to a valid address).

When user submits multiple descriptors on the recv side, with the
Current driver flow the last buffer descriptor next descriptor field
Points to a invalid location, resulting the invalid data or errors in the
DMA engine.

This patch fixes this issue by creating a Buffer Descritpor Chain during
Channel allocation itself and use those Buffer Descriptors.

Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
---
Changes for v6:
---> Updated Commit message as suggested by Vinod.
Changes for v5:
---> None.
Changes for v4:
---> None.
Changes for v3:
---> None.
Changes for v2:
---> None.

 drivers/dma/xilinx/xilinx_dma.c | 133 +++++++++++++++++++++++++---------------
 1 file changed, 83 insertions(+), 50 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index edb5b71..c5cd935 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -163,6 +163,7 @@
 #define XILINX_DMA_BD_SOP		BIT(27)
 #define XILINX_DMA_BD_EOP		BIT(26)
 #define XILINX_DMA_COALESCE_MAX		255
+#define XILINX_DMA_NUM_DESCS		255
 #define XILINX_DMA_NUM_APP_WORDS	5
 
 /* Multi-Channel DMA Descriptor offsets*/
@@ -310,6 +311,7 @@ struct xilinx_dma_tx_descriptor {
  * @pending_list: Descriptors waiting
  * @active_list: Descriptors ready to submit
  * @done_list: Complete descriptors
+ * @free_seg_list: Free descriptors
  * @common: DMA common channel
  * @desc_pool: Descriptors pool
  * @dev: The dma device
@@ -331,7 +333,9 @@ struct xilinx_dma_tx_descriptor {
  * @desc_submitcount: Descriptor h/w submitted count
  * @residue: Residue for AXI DMA
  * @seg_v: Statically allocated segments base
+ * @seg_p: Physical allocated segments base
  * @cyclic_seg_v: Statically allocated segment base for cyclic transfers
+ * @cyclic_seg_p: Physical allocated segments base for cyclic dma
  * @start_transfer: Differentiate b/w DMA IP's transfer
  */
 struct xilinx_dma_chan {
@@ -342,6 +346,7 @@ struct xilinx_dma_chan {
 	struct list_head pending_list;
 	struct list_head active_list;
 	struct list_head done_list;
+	struct list_head free_seg_list;
 	struct dma_chan common;
 	struct dma_pool *desc_pool;
 	struct device *dev;
@@ -363,7 +368,9 @@ struct xilinx_dma_chan {
 	u32 desc_submitcount;
 	u32 residue;
 	struct xilinx_axidma_tx_segment *seg_v;
+	dma_addr_t seg_p;
 	struct xilinx_axidma_tx_segment *cyclic_seg_v;
+	dma_addr_t cyclic_seg_p;
 	void (*start_transfer)(struct xilinx_dma_chan *chan);
 	u16 tdest;
 };
@@ -569,17 +576,31 @@ static struct xilinx_axidma_tx_segment *
 xilinx_axidma_alloc_tx_segment(struct xilinx_dma_chan *chan)
 {
 	struct xilinx_axidma_tx_segment *segment;
-	dma_addr_t phys;
-
-	segment = dma_pool_zalloc(chan->desc_pool, GFP_ATOMIC, &phys);
-	if (!segment)
-		return NULL;
+	unsigned long flags;
 
-	segment->phys = phys;
+	spin_lock_irqsave(&chan->lock, flags);
+	if (!list_empty(&chan->free_seg_list)) {
+		segment = list_first_entry(&chan->free_seg_list,
+					   struct xilinx_axidma_tx_segment,
+					   node);
+		list_del(&segment->node);
+	}
+	spin_unlock_irqrestore(&chan->lock, flags);
 
 	return segment;
 }
 
+static void xilinx_dma_clean_hw_desc(struct xilinx_axidma_desc_hw *hw)
+{
+	u32 next_desc = hw->next_desc;
+	u32 next_desc_msb = hw->next_desc_msb;
+
+	memset(hw, 0, sizeof(struct xilinx_axidma_desc_hw));
+
+	hw->next_desc = next_desc;
+	hw->next_desc_msb = next_desc_msb;
+}
+
 /**
  * xilinx_dma_free_tx_segment - Free transaction segment
  * @chan: Driver specific DMA channel
@@ -588,7 +609,9 @@ xilinx_axidma_alloc_tx_segment(struct xilinx_dma_chan *chan)
 static void xilinx_dma_free_tx_segment(struct xilinx_dma_chan *chan,
 				struct xilinx_axidma_tx_segment *segment)
 {
-	dma_pool_free(chan->desc_pool, segment, segment->phys);
+	xilinx_dma_clean_hw_desc(&segment->hw);
+
+	list_add_tail(&segment->node, &chan->free_seg_list);
 }
 
 /**
@@ -713,16 +736,26 @@ static void xilinx_dma_free_descriptors(struct xilinx_dma_chan *chan)
 static void xilinx_dma_free_chan_resources(struct dma_chan *dchan)
 {
 	struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
+	unsigned long flags;
 
 	dev_dbg(chan->dev, "Free all channel resources.\n");
 
 	xilinx_dma_free_descriptors(chan);
+
 	if (chan->xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
-		xilinx_dma_free_tx_segment(chan, chan->cyclic_seg_v);
-		xilinx_dma_free_tx_segment(chan, chan->seg_v);
+		spin_lock_irqsave(&chan->lock, flags);
+		INIT_LIST_HEAD(&chan->free_seg_list);
+		spin_unlock_irqrestore(&chan->lock, flags);
+
+		/* Free Memory that is allocated for cyclic DMA Mode */
+		dma_free_coherent(chan->dev, sizeof(*chan->cyclic_seg_v),
+				  chan->cyclic_seg_v, chan->cyclic_seg_p);
+	}
+
+	if (chan->xdev->dma_config->dmatype != XDMA_TYPE_AXIDMA) {
+		dma_pool_destroy(chan->desc_pool);
+		chan->desc_pool = NULL;
 	}
-	dma_pool_destroy(chan->desc_pool);
-	chan->desc_pool = NULL;
 }
 
 /**
@@ -805,6 +838,7 @@ static void xilinx_dma_do_tasklet(unsigned long data)
 static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
 {
 	struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
+	int i;
 
 	/* Has this channel already been allocated? */
 	if (chan->desc_pool)
@@ -815,11 +849,30 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
 	 * for meeting Xilinx VDMA specification requirement.
 	 */
 	if (chan->xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
-		chan->desc_pool = dma_pool_create("xilinx_dma_desc_pool",
-				   chan->dev,
-				   sizeof(struct xilinx_axidma_tx_segment),
-				   __alignof__(struct xilinx_axidma_tx_segment),
-				   0);
+		/* Allocate the buffer descriptors. */
+		chan->seg_v = dma_zalloc_coherent(chan->dev,
+						  sizeof(*chan->seg_v) *
+						  XILINX_DMA_NUM_DESCS,
+						  &chan->seg_p, GFP_KERNEL);
+		if (!chan->seg_v) {
+			dev_err(chan->dev,
+				"unable to allocate channel %d descriptors\n",
+				chan->id);
+			return -ENOMEM;
+		}
+
+		for (i = 0; i < XILINX_DMA_NUM_DESCS; i++) {
+			chan->seg_v[i].hw.next_desc =
+			lower_32_bits(chan->seg_p + sizeof(*chan->seg_v) *
+				((i + 1) % XILINX_DMA_NUM_DESCS));
+			chan->seg_v[i].hw.next_desc_msb =
+			upper_32_bits(chan->seg_p + sizeof(*chan->seg_v) *
+				((i + 1) % XILINX_DMA_NUM_DESCS));
+			chan->seg_v[i].phys = chan->seg_p +
+				sizeof(*chan->seg_v) * i;
+			list_add_tail(&chan->seg_v[i].node,
+				      &chan->free_seg_list);
+		}
 	} else if (chan->xdev->dma_config->dmatype == XDMA_TYPE_CDMA) {
 		chan->desc_pool = dma_pool_create("xilinx_cdma_desc_pool",
 				   chan->dev,
@@ -834,7 +887,8 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
 				     0);
 	}
 
-	if (!chan->desc_pool) {
+	if (!chan->desc_pool &&
+	    (chan->xdev->dma_config->dmatype != XDMA_TYPE_AXIDMA)) {
 		dev_err(chan->dev,
 			"unable to allocate channel %d descriptor pool\n",
 			chan->id);
@@ -843,22 +897,20 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
 
 	if (chan->xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
 		/*
-		 * For AXI DMA case after submitting a pending_list, keep
-		 * an extra segment allocated so that the "next descriptor"
-		 * pointer on the tail descriptor always points to a
-		 * valid descriptor, even when paused after reaching taildesc.
-		 * This way, it is possible to issue additional
-		 * transfers without halting and restarting the channel.
-		 */
-		chan->seg_v = xilinx_axidma_alloc_tx_segment(chan);
-
-		/*
 		 * For cyclic DMA mode we need to program the tail Descriptor
 		 * register with a value which is not a part of the BD chain
 		 * so allocating a desc segment during channel allocation for
 		 * programming tail descriptor.
 		 */
-		chan->cyclic_seg_v = xilinx_axidma_alloc_tx_segment(chan);
+		chan->cyclic_seg_v = dma_zalloc_coherent(chan->dev,
+					sizeof(*chan->cyclic_seg_v),
+					&chan->cyclic_seg_p, GFP_KERNEL);
+		if (!chan->cyclic_seg_v) {
+			dev_err(chan->dev,
+				"unable to allocate desc segment for cyclic DMA\n");
+			return -ENOMEM;
+		}
+		chan->cyclic_seg_v->phys = chan->cyclic_seg_p;
 	}
 
 	dma_cookie_init(dchan);
@@ -1198,7 +1250,7 @@ static void xilinx_cdma_start_transfer(struct xilinx_dma_chan *chan)
 static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 {
 	struct xilinx_dma_tx_descriptor *head_desc, *tail_desc;
-	struct xilinx_axidma_tx_segment *tail_segment, *old_head, *new_head;
+	struct xilinx_axidma_tx_segment *tail_segment;
 	u32 reg;
 
 	if (chan->err)
@@ -1217,21 +1269,6 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 	tail_segment = list_last_entry(&tail_desc->segments,
 				       struct xilinx_axidma_tx_segment, node);
 
-	if (chan->has_sg && !chan->xdev->mcdma) {
-		old_head = list_first_entry(&head_desc->segments,
-					struct xilinx_axidma_tx_segment, node);
-		new_head = chan->seg_v;
-		/* Copy Buffer Descriptor fields. */
-		new_head->hw = old_head->hw;
-
-		/* Swap and save new reserve */
-		list_replace_init(&old_head->node, &new_head->node);
-		chan->seg_v = old_head;
-
-		tail_segment->hw.next_desc = chan->seg_v->phys;
-		head_desc->async_tx.phys = new_head->phys;
-	}
-
 	reg = dma_ctrl_read(chan, XILINX_DMA_REG_DMACR);
 
 	if (chan->desc_pendingcount <= XILINX_DMA_COALESCE_MAX) {
@@ -1729,7 +1766,7 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
 {
 	struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
 	struct xilinx_dma_tx_descriptor *desc;
-	struct xilinx_axidma_tx_segment *segment = NULL, *prev = NULL;
+	struct xilinx_axidma_tx_segment *segment = NULL;
 	u32 *app_w = (u32 *)context;
 	struct scatterlist *sg;
 	size_t copy;
@@ -1780,10 +1817,6 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
 					       XILINX_DMA_NUM_APP_WORDS);
 			}
 
-			if (prev)
-				prev->hw.next_desc = segment->phys;
-
-			prev = segment;
 			sg_used += copy;
 
 			/*
@@ -1797,7 +1830,6 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
 	segment = list_first_entry(&desc->segments,
 				   struct xilinx_axidma_tx_segment, node);
 	desc->async_tx.phys = segment->phys;
-	prev->hw.next_desc = segment->phys;
 
 	/* For the last DMA_MEM_TO_DEV transfer, set EOP */
 	if (chan->direction == DMA_MEM_TO_DEV) {
@@ -2346,6 +2378,7 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
 	INIT_LIST_HEAD(&chan->pending_list);
 	INIT_LIST_HEAD(&chan->done_list);
 	INIT_LIST_HEAD(&chan->active_list);
+	INIT_LIST_HEAD(&chan->free_seg_list);
 
 	/* Retrieve the channel properties from the device tree */
 	has_dre = of_property_read_bool(node, "xlnx,include-dre");
-- 
2.1.2