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

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  Re: [PATCH 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2016-12-16 16:40 +0100
    Re: [PATCH 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2016-12-19 18:20 +0100

#1543529 — Re: [PATCH 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

Hi Kedareswara,

Thank you for the patch.

On Thursday 15 Dec 2016 20:41:20 Kedareswara rao Appana wrote:
> Add channel idle state to ensure that dma descriptor is not
> submitted when VDMA engine is in progress.
>
> Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
> ---
>  drivers/dma/xilinx/xilinx_dma.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/dma/xilinx/xilinx_dma.c
> b/drivers/dma/xilinx/xilinx_dma.c index 8288fe4..736c2a3 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;
> @@ -966,6 +968,7 @@ 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 +1010,9 @@ static void xilinx_vdma_start_transfer(struct
> xilinx_dma_chan *chan)
> 	if (chan->err)
>  		return;
> 
> +	if (!chan->idle)
> +		return;

Don't you need to perform the same check for the DMA and CDMA channels ? If 
so, shouldn't this be moved to common code ?

There's another problem (not strictly introduced by this patch) I wanted to 
mention. The append_desc_queue() function, called from your tx_submit handler, 
appends descriptors to the pending_list. The DMA engine API states that a 
transfer submitted by tx_submit will not be executed until .issue_pending() is 
called. However, if a transfer is in progress at tx_submit time, I believe 
that the IRQ handler, at transfer completion, will start the next transfer 
from the pending_list even if .issue_pending() hasn't been called for it.

>  	if (list_empty(&chan->pending_list))
>  		return;

Now that you catch busy channels with a software flag, do you still need the 
xilinx_dma_is_running() and xilinx_dma_is_idle() checks ? Three different 
checks for the same or very similar conditions are confusing, if you really 
need them you should document clearly how they differ.

> @@ -1110,6 +1116,7 @@ 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;

(and this too)

>  	if (!chan->has_sg) {
>  		list_del(&desc->node);
>  		list_add_tail(&desc->node, &chan->active_list);
> @@ -1447,6 +1454,7 @@ 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 +2335,7 @@ 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);

-- 
Regards,

Laurent Pinchart

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#1544684

Hi Kedar,

On Monday 19 Dec 2016 15:39:43 Appana Durga Kedareswara Rao wrote:
> Hi Laurent Pinchart,
> 
> 	Thanks for the review...
> 
> > > +	if (!chan->idle)
> > > +		return;
> > 
> > Don't you need to perform the same check for the DMA and CDMA channels ?
> > If so, shouldn't this be moved to common code ?
> 
> Will fix it in v2...
> 
> > There's another problem (not strictly introduced by this patch) I wanted
> > to mention. The append_desc_queue() function, called from your tx_submit
> > handler, appends descriptors to the pending_list. The DMA engine API
> > states that a transfer submitted by tx_submit will not be executed until
> > .issue_pending() is called. However, if a transfer is in progress at
> > tx_submit time, I believe that the IRQ handler, at transfer completion,
> > will start the next transfer from the pending_list even if
> > .issue_pending() hasn't been called for it.
> > 
> > >  	if (list_empty(&chan->pending_list))
> > >  		return;
> 
> If user submits more than h/w limit then that case only driver will process
> The descriptors from the pending_list for other cases the pending_list will
> be Empty so driver just returns from there.

I understand that, but that's not the problem. Your .tx_submit() handler calls 
append_desc_queue() which adds the tx descriptor to the pending_list. If a 
transfer is in progress at that time, I believe the transfer completion IRQ 
handler will take the next descriptor from the pending_list and process it, 
even though issue_pending() hasn't been called for it.

> > Now that you catch busy channels with a software flag, do you still need
> > the xilinx_dma_is_running() and xilinx_dma_is_idle() checks ? Three
> > different checks for the same or very similar conditions are confusing,
> > if you really need them you should document clearly how they differ.
> 
> Will remove the xilinx_dma_is_running and xilinx_dmais_idle() checks and
> will use Chan->idle check across all the IP's. Will fix it v2...
> 
> > > @@ -1110,6 +1116,7 @@ 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;
> > 
> > (and this too)
> 
> Will fix in v2...

-- 
Regards,

Laurent Pinchart

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