[PATCH v5 0/3] dmaengine: xilinx_dma: Bug fixes

[PATCH v5 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                    | 265 ++++++++++++---------
 2 files changed, 156 insertions(+), 111 deletions(-)

-- 
2.1.2

[PATCH v5 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

[Kedareswara rao Appana]

Add channel idle state to ensure that dma descriptor is not
submitted when VDMA engine is in progress.

Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
---
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 | 56 +++++++++++++----------------------------
 1 file changed, 17 insertions(+), 39 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 8288fe4..be7eb41 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 +2304,7 @@ 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;
+	chan->idle = true;
 
 	spin_lock_init(&chan->lock);
 	INIT_LIST_HEAD(&chan->pending_list);
-- 
2.1.2

[PATCH v5 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

[Vinod Koul]

On Sat, Jan 07, 2017 at 12:15:28PM +0530, Kedareswara rao Appana wrote:
> Add channel idle state to ensure that dma descriptor is not
> submitted when VDMA engine is in progress.

any reason why you want to make your own varible and not use the HW to query
as done earlier. It is not clear to me why that is removed from description

> 
> Reviewed-by: Jose Abreu <joabreu@synopsys.com>
> Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> ---
> 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 | 56 +++++++++++++----------------------------
>  1 file changed, 17 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index 8288fe4..be7eb41 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 +2304,7 @@ 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;
> +	chan->idle = true;
>  
>  	spin_lock_init(&chan->lock);
>  	INIT_LIST_HEAD(&chan->pending_list);
> -- 
> 2.1.2
> 

-- 
~Vinod

[PATCH v5 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

[Appana Durga Kedareswara Rao]

Hi Vinod,

	Thanks for the review...
> 
> On Sat, Jan 07, 2017 at 12:15:28PM +0530, Kedareswara rao Appana wrote:
> > Add channel idle state to ensure that dma descriptor is not
> > submitted when VDMA engine is in progress.
> 
> any reason why you want to make your own varible and not use the HW to
> query
> as done earlier. It is not clear to me why that is removed from description

We need to poll for a bit in the status register to know the dma state.
We are currently doing that in the driver hot path
To avoid this using own variables.

Regards,
Kedar.

[PATCH v5 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

[Vinod Koul]

On Fri, Jan 13, 2017 at 04:28:11AM +0000, Appana Durga Kedareswara Rao wrote:
> Hi Vinod,
> 
> 	Thanks for the review...
> > 
> > On Sat, Jan 07, 2017 at 12:15:28PM +0530, Kedareswara rao Appana wrote:
> > > Add channel idle state to ensure that dma descriptor is not
> > > submitted when VDMA engine is in progress.
> > 
> > any reason why you want to make your own varible and not use the HW to
> > query
> > as done earlier. It is not clear to me why that is removed from description
> 
> We need to poll for a bit in the status register to know the dma state.
> We are currently doing that in the driver hot path
> To avoid this using own variables.

It would be worthwhile to document these, down the line people may not
remeber the motivation


-- 
~Vinod

[PATCH v5 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

[Appana Durga Kedareswara Rao]

Hi Vinod,
	
	Thanks for the review...
> 
> On Fri, Jan 13, 2017 at 04:28:11AM +0000, Appana Durga Kedareswara Rao
> wrote:
> > Hi Vinod,
> >
> > 	Thanks for the review...
> > >
> > > On Sat, Jan 07, 2017 at 12:15:28PM +0530, Kedareswara rao Appana wrote:
> > > > Add channel idle state to ensure that dma descriptor is not
> > > > submitted when VDMA engine is in progress.
> > >
> > > any reason why you want to make your own varible and not use the HW
> > > to query as done earlier. It is not clear to me why that is removed
> > > from description
> >
> > We need to poll for a bit in the status register to know the dma state.
> > We are currently doing that in the driver hot path To avoid this using
> > own variables.
> 
> It would be worthwhile to document these, down the line people may not
> remeber the motivation

Sure will add comments during the variable initialization
In the driver...

Regards,
Kedar.

> 
> 
> --
> ~Vinod

[PATCH v5 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 and 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.

Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
---
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 be7eb41..0e9c02e 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;
 }
@@ -2315,6 +2346,7 @@ 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 v5 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

[Rob Herring]

On Sat, Jan 07, 2017 at 12:15:29PM +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 and 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.
> 
> Reviewed-by: Jose Abreu <joabreu@synopsys.com>
> Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> ---
> 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 +

Acked-by: Rob Herring <robh@kernel.org>

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

[PATCH v5 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

[Vinod Koul]

On Sat, Jan 07, 2017 at 12:15:29PM +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 and user
> Submits n number of frames and triggered the DMA using issue_pending API.

title case in middle if sentence, no commas, can you make it easier to read
please..

> 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.

s/Is/is

> 
> This patch fixes this issue.
> 
> Reviewed-by: Jose Abreu <joabreu@synopsys.com>
> Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> ---
> 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 be7eb41..0e9c02e 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;
>  }
> @@ -2315,6 +2346,7 @@ 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 v5 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

[Appana Durga Kedareswara Rao]

Hi Vinod,

	Thanks for the review...  

> 
> On Sat, Jan 07, 2017 at 12:15:29PM +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 and user Submits n number of
> > frames and triggered the DMA using issue_pending API.
> 
> title case in middle if sentence, no commas, can you make it easier to read
> please..

Ok sure will fix commit message in the next version.

> 
> > 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.
> 
> s/Is/is

Ok sure will fix in the next version....

Regards,
Kedar.

[PATCH v5 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Kedareswara rao Appana]

When driver is handling AXI DMA SoftIP
When user submits multiple descriptors back to back on the S2MM(recv)
side with the current driver flow the last buffer descriptor next bd
points to a invalid location resulting the invalid data or errors in the
DMA engine.

This patch fixes this issue by creating a BD Chain during
channel allocation itself and use those BD's.

Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
---
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 0e9c02e..af2159d 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) {
@@ -2341,6 +2373,7 @@ 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

[PATCH v5 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Vinod Koul]

On Sat, Jan 07, 2017 at 12:15:30PM +0530, Kedareswara rao Appana wrote:
> When driver is handling AXI DMA SoftIP
> When user submits multiple descriptors back to back on the S2MM(recv)
> side with the current driver flow the last buffer descriptor next bd
> points to a invalid location resulting the invalid data or errors in the
> DMA engine.

Can you rephrase this, it a bit hard to understand.

> 
> This patch fixes this issue by creating a BD Chain during

whats a BD?

> channel allocation itself and use those BD's.
> 
> Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> ---
> 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 0e9c02e..af2159d 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

why 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) {
> @@ -2341,6 +2373,7 @@ 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
> 

-- 
~Vinod

[PATCH v5 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Appana Durga Kedareswara Rao]

Hi Vinod,

	Thanks for the review...    

> On Sat, Jan 07, 2017 at 12:15:30PM +0530, Kedareswara rao Appana wrote:
> > When driver is handling AXI DMA SoftIP When user submits multiple
> > descriptors back to back on the S2MM(recv) side with the current
> > driver flow the last buffer descriptor next bd points to a invalid
> > location resulting the invalid data or errors in the DMA engine.
> 
> Can you rephrase this, it a bit hard to understand.

When DMA is receiving packets h/w expects the descriptors
Should be in the form of a ring (I mean h/w buffer descriptor
Next descriptor field should always point to valid address
So that when DMA engine go and fetch that next descriptor it always 
Sees a valid address).

But with the current driver implementation when user queues
Multiple descriptors the last descriptor next descriptor field
Pointing to an invalid location causing data corruption or 
Errors from the DMA h/w engine...

To avoid this issue creating a Buffer descriptor Chain during 
Channel allocation and using those buffer descriptors for processing
User requested data.

Please let me know if the above explanation is not clear will explain in detail....

> 
> >
> > This patch fixes this issue by creating a BD Chain during
> 
> whats a BD?

Buffer descriptor.

> 
> > channel allocation itself and use those BD's.
> >
> > Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> > ---
> >
> >  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 0e9c02e..af2159d 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
> 
> why 255?

It is not an h/w limitation 
Allocating 255 descriptors (Each descriptor is capable of sending 7MB data)
So roughly using allocated descriptors DMA engine can transfer 1GB data
And in the driver we are reusing the allocated descriptors when they are free.

Regards,
Kedar.

[PATCH v5 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Vinod Koul]

On Thu, Jan 12, 2017 at 02:19:49PM +0000, Appana Durga Kedareswara Rao wrote:
> Hi Vinod,
> 
> 	Thanks for the review...    
> 
> > On Sat, Jan 07, 2017 at 12:15:30PM +0530, Kedareswara rao Appana wrote:
> > > When driver is handling AXI DMA SoftIP When user submits multiple
> > > descriptors back to back on the S2MM(recv) side with the current
> > > driver flow the last buffer descriptor next bd points to a invalid
> > > location resulting the invalid data or errors in the DMA engine.
> > 
> > Can you rephrase this, it a bit hard to understand.
> 
> When DMA is receiving packets h/w expects the descriptors
> Should be in the form of a ring (I mean h/w buffer descriptor
> Next descriptor field should always point to valid address
> So that when DMA engine go and fetch that next descriptor it always 
> Sees a valid address).
>
> 
> But with the current driver implementation when user queues
> Multiple descriptors the last descriptor next descriptor field
> Pointing to an invalid location causing data corruption or 
> Errors from the DMA h/w engine...
> 
> To avoid this issue creating a Buffer descriptor Chain during 
> Channel allocation and using those buffer descriptors for processing
> User requested data.

Is it not doable to to modify the next pointer to point to subsequent
transaction. IOW you are modifying tail descriptor to point to subsequent
descriptor.

Btw how and when does DMA stop, assuming it is circular it never would,
isn't there a valid/stop flag associated with a descriptor which tells DMA
engine what to do next


Btw there is something wrong with your MUA perhaps line are titlecased for
no reason. This is typically behavious of non linux tool which may not be
great tool for this work.

> 
> Please let me know if the above explanation is not clear will explain in detail....
> 
> > 
> > >
> > > This patch fixes this issue by creating a BD Chain during
> > 
> > whats a BD?
> 
> Buffer descriptor.

Thats nowhere mentioned..

> 
> > 
> > > channel allocation itself and use those BD's.
> > >
> > > Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> > > ---
> > >
> > >  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 0e9c02e..af2159d 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
> > 
> > why 255?
> 
> It is not an h/w limitation 
> Allocating 255 descriptors (Each descriptor is capable of sending 7MB data)
> So roughly using allocated descriptors DMA engine can transfer 1GB data
> And in the driver we are reusing the allocated descriptors when they are free.
> 
> Regards,
> Kedar.

-- 
~Vinod

[PATCH v5 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Appana Durga Kedareswara Rao]

Hi Vinod,

	Thanks for the review...

[Snip]
> >
> > > On Sat, Jan 07, 2017 at 12:15:30PM +0530, Kedareswara rao Appana wrote:
> > > > When driver is handling AXI DMA SoftIP When user submits multiple
> > > > descriptors back to back on the S2MM(recv) side with the current
> > > > driver flow the last buffer descriptor next bd points to a invalid
> > > > location resulting the invalid data or errors in the DMA engine.
> > >
> > > Can you rephrase this, it a bit hard to understand.
> >
> > When DMA is receiving packets h/w expects the descriptors Should be in
> > the form of a ring (I mean h/w buffer descriptor Next descriptor field
> > should always point to valid address So that when DMA engine go and
> > fetch that next descriptor it always Sees a valid address).
> >
> >
> > But with the current driver implementation when user queues Multiple
> > descriptors the last descriptor next descriptor field Pointing to an
> > invalid location causing data corruption or Errors from the DMA h/w
> > engine...
> >
> > To avoid this issue creating a Buffer descriptor Chain during Channel
> > allocation and using those buffer descriptors for processing User
> > requested data.
> 
> Is it not doable to to modify the next pointer to point to subsequent transaction.
> IOW you are modifying tail descriptor to point to subsequent descriptor.
> 
> Btw how and when does DMA stop, assuming it is circular it never would, isn't
> there a valid/stop flag associated with a descriptor which tells DMA engine what
> to do next

There are two registers that controls the DMA transfers.
Current descriptor and tail descriptor register. 
When current descriptor reaches tail descriptor dma engine will pause.

When reprogramming the tail descriptor the DMA engine will starts fetching descriptors again.

But with the existing driver flow if we reprogram the tail descriptor
The tail descriptor next descriptor field is pointing to an invalid location
Causing data corruption...

> 
> 
> Btw there is something wrong with your MUA perhaps line are titlecased for no
> reason. This is typically behavious of non linux tool which may not be great tool
> for this work.

Thanks for pointing it out.
I usually replies from outlook from a windows machine.
Will check with others in my team how they configured their mail client.

> 
> >
> > Please let me know if the above explanation is not clear will explain in detail....
> >
> > >
> > > >
> > > > This patch fixes this issue by creating a BD Chain during
> > >
> > > whats a BD?
> >
> > Buffer descriptor.
> 
> Thats nowhere mentioned..

Yep sorry I should have been mentioned it...

Regards,
Kedar.

[PATCH v5 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Vinod Koul]

On Fri, Jan 13, 2017 at 06:00:44AM +0000, Appana Durga Kedareswara Rao wrote:
> Hi Vinod,
> 
> 	Thanks for the review...
> 
> [Snip]
> > >
> > > > On Sat, Jan 07, 2017 at 12:15:30PM +0530, Kedareswara rao Appana wrote:
> > > > > When driver is handling AXI DMA SoftIP When user submits multiple
> > > > > descriptors back to back on the S2MM(recv) side with the current
> > > > > driver flow the last buffer descriptor next bd points to a invalid
> > > > > location resulting the invalid data or errors in the DMA engine.
> > > >
> > > > Can you rephrase this, it a bit hard to understand.
> > >
> > > When DMA is receiving packets h/w expects the descriptors Should be in
> > > the form of a ring (I mean h/w buffer descriptor Next descriptor field
> > > should always point to valid address So that when DMA engine go and
> > > fetch that next descriptor it always Sees a valid address).
> > >
> > >
> > > But with the current driver implementation when user queues Multiple
> > > descriptors the last descriptor next descriptor field Pointing to an
> > > invalid location causing data corruption or Errors from the DMA h/w
> > > engine...
> > >
> > > To avoid this issue creating a Buffer descriptor Chain during Channel
> > > allocation and using those buffer descriptors for processing User
> > > requested data.
> > 
> > Is it not doable to to modify the next pointer to point to subsequent transaction.
> > IOW you are modifying tail descriptor to point to subsequent descriptor.
> > 
> > Btw how and when does DMA stop, assuming it is circular it never would, isn't
> > there a valid/stop flag associated with a descriptor which tells DMA engine what
> > to do next
> 
> There are two registers that controls the DMA transfers.
> Current descriptor and tail descriptor register. 
> When current descriptor reaches tail descriptor dma engine will pause.
> 
> When reprogramming the tail descriptor the DMA engine will starts fetching descriptors again.
> 
> But with the existing driver flow if we reprogram the tail descriptor
> The tail descriptor next descriptor field is pointing to an invalid location
> Causing data corruption...

So the solution is..?

> > Btw there is something wrong with your MUA perhaps line are titlecased for no
> > reason. This is typically behavious of non linux tool which may not be great tool
> > for this work.
> 
> Thanks for pointing it out.
> I usually replies from outlook from a windows machine.
> Will check with others in my team how they configured their mail client.

Yeah that isnt right tool for the job. See
Documentation/process/email-clients.rst

FWIW, I use mutt, vim as editor with exchange servers, seems to work well
for me now.

-- 
~Vinod

[PATCH v5 3/3] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario

[Appana Durga Kedareswara Rao]

Hi Vinod,
	
	Thanks for the review...

[Snip]
> > > Btw how and when does DMA stop, assuming it is circular it never
> > > would, isn't there a valid/stop flag associated with a descriptor
> > > which tells DMA engine what to do next
> >
> > There are two registers that controls the DMA transfers.
> > Current descriptor and tail descriptor register.
> > When current descriptor reaches tail descriptor dma engine will pause.
> >
> > When reprogramming the tail descriptor the DMA engine will starts fetching
> descriptors again.
> >
> > But with the existing driver flow if we reprogram the tail descriptor
> > The tail descriptor next descriptor field is pointing to an invalid
> > location Causing data corruption...
> 
> So the solution is..?

This patch.
I mean if we have a set of descriptors in chain (in circular manner last descriptor points to first descriptor)
It always points to valid descriptors. 

Will update the patch commit description in the next version...

> 
> > > Btw there is something wrong with your MUA perhaps line are
> > > titlecased for no reason. This is typically behavious of non linux
> > > tool which may not be great tool for this work.
> >
> > Thanks for pointing it out.
> > I usually replies from outlook from a windows machine.
> > Will check with others in my team how they configured their mail client.
> 
> Yeah that isnt right tool for the job. See Documentation/process/email-
> clients.rst
> 
> FWIW, I use mutt, vim as editor with exchange servers, seems to work well for
> me now.

Thanks for pointing it out will go through it.
Will install mutt in my Linux machine will start replying from that

Regards,
Kedar.

> 
> --
> ~Vinod