linux-kernel - Re: [PATCH v2 2/4] dmaengine: xilinx

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Message-ID: <20160223030937.GH17690@localhost>
Date:	Tue, 23 Feb 2016 08:39:37 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Kedareswara rao Appana <appana.durga.rao@...inx.com>
Cc:	dan.j.williams@...el.com, michal.simek@...inx.com,
	soren.brinkmann@...inx.com, appanad@...inx.com,
	moritz.fischer@...us.com, laurent.pinchart@...asonboard.com,
	luis@...ethencourt.com, anirudh@...inx.com,
	dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] dmaengine: xilinx_vdma: Simplify spin lock
 handling

On Mon, Feb 22, 2016 at 11:24:35AM +0530, Kedareswara rao Appana wrote:
> This patch simplifies the spin lock handling in the driver.

But sadly doesn't describe how?

> 
> Signed-off-by: Kedareswara rao Appana <appanad@...inx.com>
> ---
> Changes for v2:
> ---> splitted the changes into multiple patches.
> 
>  drivers/dma/xilinx/xilinx_vdma.c | 27 ++++++++++-----------------
>  1 file changed, 10 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/dma/xilinx/xilinx_vdma.c b/drivers/dma/xilinx/xilinx_vdma.c
> index 06bffec..d646218 100644
> --- a/drivers/dma/xilinx/xilinx_vdma.c
> +++ b/drivers/dma/xilinx/xilinx_vdma.c
> @@ -605,17 +605,14 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
>  {
>  	struct xilinx_vdma_config *config = &chan->config;
>  	struct xilinx_vdma_tx_descriptor *desc, *tail_desc;
> -	unsigned long flags;
>  	u32 reg;
>  	struct xilinx_vdma_tx_segment *tail_segment;
>  
>  	if (chan->err)
>  		return;
>  
> -	spin_lock_irqsave(&chan->lock, flags);
> -

It would help if you add a comment to this function taht we need to invoke
this with lock held...

>  	if (list_empty(&chan->pending_list))
> -		goto out_unlock;
> +		return;
>  
>  	desc = list_first_entry(&chan->pending_list,
>  				struct xilinx_vdma_tx_descriptor, node);
> @@ -629,7 +626,7 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
>  	if (chan->has_sg && xilinx_vdma_is_running(chan) &&
>  	    !xilinx_vdma_is_idle(chan)) {
>  		dev_dbg(chan->dev, "DMA controller still busy\n");
> -		goto out_unlock;
> +		return;
>  	}
>  
>  	/*
> @@ -676,7 +673,7 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
>  	xilinx_vdma_start(chan);
>  
>  	if (chan->err)
> -		goto out_unlock;
> +		return;
>  
>  	/* Start the transfer */
>  	if (chan->has_sg) {
> @@ -696,7 +693,7 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
>  		}
>  
>  		if (!last)
> -			goto out_unlock;
> +			return;
>  
>  		/* HW expects these parameters to be same for one transaction */
>  		vdma_desc_write(chan, XILINX_VDMA_REG_HSIZE, last->hw.hsize);
> @@ -707,9 +704,6 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
>  
>  	list_splice_tail_init(&chan->pending_list, &chan->active_list);
>  	chan->desc_pendingcount = 0;
> -
> -out_unlock:
> -	spin_unlock_irqrestore(&chan->lock, flags);
>  }
>  
>  /**
> @@ -719,8 +713,11 @@ out_unlock:
>  static void xilinx_vdma_issue_pending(struct dma_chan *dchan)
>  {
>  	struct xilinx_vdma_chan *chan = to_xilinx_chan(dchan);
> +	unsigned long flags;
>  
> +	spin_lock_irqsave(&chan->lock, flags);
>  	xilinx_vdma_start_transfer(chan);
> +	spin_unlock_irqrestore(&chan->lock, flags);
>  }
>  
>  /**
> @@ -732,21 +729,15 @@ static void xilinx_vdma_issue_pending(struct dma_chan *dchan)
>  static void xilinx_vdma_complete_descriptor(struct xilinx_vdma_chan *chan)
>  {
>  	struct xilinx_vdma_tx_descriptor *desc, *next;
> -	unsigned long flags;
> -
> -	spin_lock_irqsave(&chan->lock, flags);

this one as well

>  
>  	if (list_empty(&chan->active_list))
> -		goto out_unlock;
> +		return;
>  
>  	list_for_each_entry_safe(desc, next, &chan->active_list, node) {
>  		list_del(&desc->node);
>  		dma_cookie_complete(&desc->async_tx);
>  		list_add_tail(&desc->node, &chan->done_list);
>  	}
> -
> -out_unlock:
> -	spin_unlock_irqrestore(&chan->lock, flags);
>  }
>  
>  /**
> @@ -857,8 +848,10 @@ static irqreturn_t xilinx_vdma_irq_handler(int irq, void *data)
>  	}
>  
>  	if (status & XILINX_VDMA_DMASR_FRM_CNT_IRQ) {
> +		spin_lock(&chan->lock);
>  		xilinx_vdma_complete_descriptor(chan);
>  		xilinx_vdma_start_transfer(chan);
> +		spin_unlock(&chan->lock);
>  	}
>  
>  	tasklet_schedule(&chan->tasklet);
> -- 
> 2.1.2
> 
> --
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-- 
~Vinod