Subject: Re: [PATCH v5 5/6] fsl-dma: use spin_lock_bh to instead of spin_lock_irqsave

From: "Ira W. Snyder" <[email-masked]>
Date: Wed, 1 Aug 2012 10:30:59 -0700

On Wed, Aug 01, 2012 at 04:50:09PM +0800, [email-masked] wrote:
> From: Qiang Liu <[email-masked]>
> 
> - use spin_lock_bh() is the right way to use async_tx api,
> dma_run_dependencies() should not be protected by spin_lock_irqsave();
> - use spin_lock_bh to instead of spin_lock_irqsave for improving performance,
> There is not any place to access descriptor queues in fsl-dma ISR except its
> tasklet, spin_lock_bh() is more proper here. Interrupts will be turned off and
> context will be save in irqsave, there is needless to use irqsave..
> 

This description is not very clear English. I understand it is not your
native language. Let me try to help.

"""
The use of spin_lock_irqsave() is a stronger locking mechanism than is
required throughout the driver. The minimum locking required should be
used instead.

Change all instances of spin_lock_irqsave() to spin_lock_bh(). All
manipulation of protected fields is done using tasklet context or
weaker, which makes spin_lock_bh() the correct choice.
"""

Other than that,
Acked-by: Ira W. Snyder <[email-masked]>

> Cc: Dan Williams <[email-masked]>
> Cc: Vinod Koul <[email-masked]>
> Cc: Li Yang <[email-masked]>
> Cc: Timur Tabi <[email-masked]>
> Signed-off-by: Qiang Liu <[email-masked]>
> ---
>  drivers/dma/fsldma.c |   30 ++++++++++++------------------
>  1 files changed, 12 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
> index bb883c0..e3814aa 100644
> --- a/drivers/dma/fsldma.c
> +++ b/drivers/dma/fsldma.c
> @@ -645,10 +645,9 @@ static dma_cookie_t fsl_dma_tx_submit(struct dma_async_tx_descriptor *tx)
>  	struct fsldma_chan *chan = to_fsl_chan(tx->chan);
>  	struct fsl_desc_sw *desc = tx_to_fsl_desc(tx);
>  	struct fsl_desc_sw *child;
> -	unsigned long flags;
>  	dma_cookie_t cookie;
> 
> -	spin_lock_irqsave(&chan->desc_lock, flags);
> +	spin_lock_bh(&chan->desc_lock);
> 
>  	/*
>  	 * assign cookies to all of the software descriptors
> @@ -661,7 +660,7 @@ static dma_cookie_t fsl_dma_tx_submit(struct dma_async_tx_descriptor *tx)
>  	/* put this transaction onto the tail of the pending queue */
>  	append_ld_queue(chan, desc);
> 
> -	spin_unlock_irqrestore(&chan->desc_lock, flags);
> +	spin_unlock_bh(&chan->desc_lock);
> 
>  	return cookie;
>  }
> @@ -770,15 +769,14 @@ static void fsldma_free_desc_list_reverse(struct fsldma_chan *chan,
>  static void fsl_dma_free_chan_resources(struct dma_chan *dchan)
>  {
>  	struct fsldma_chan *chan = to_fsl_chan(dchan);
> -	unsigned long flags;
> 
>  	chan_dbg(chan, "free all channel resources\n");
> -	spin_lock_irqsave(&chan->desc_lock, flags);
> +	spin_lock_bh(&chan->desc_lock);
>  	fsldma_cleanup_descriptor(chan);
>  	fsldma_free_desc_list(chan, &chan->ld_pending);
>  	fsldma_free_desc_list(chan, &chan->ld_running);
>  	fsldma_free_desc_list(chan, &chan->ld_completed);
> -	spin_unlock_irqrestore(&chan->desc_lock, flags);
> +	spin_unlock_bh(&chan->desc_lock);
> 
>  	dma_pool_destroy(chan->desc_pool);
>  	chan->desc_pool = NULL;
> @@ -997,7 +995,6 @@ static int fsl_dma_device_control(struct dma_chan *dchan,
>  {
>  	struct dma_slave_config *config;
>  	struct fsldma_chan *chan;
> -	unsigned long flags;
>  	int size;
> 
>  	if (!dchan)
> @@ -1007,7 +1004,7 @@ static int fsl_dma_device_control(struct dma_chan *dchan,
> 
>  	switch (cmd) {
>  	case DMA_TERMINATE_ALL:
> -		spin_lock_irqsave(&chan->desc_lock, flags);
> +		spin_lock_bh(&chan->desc_lock);
> 
>  		/* Halt the DMA engine */
>  		dma_halt(chan);
> @@ -1017,7 +1014,7 @@ static int fsl_dma_device_control(struct dma_chan *dchan,
>  		fsldma_free_desc_list(chan, &chan->ld_running);
>  		chan->idle = true;
> 
> -		spin_unlock_irqrestore(&chan->desc_lock, flags);
> +		spin_unlock_bh(&chan->desc_lock);
>  		return 0;
> 
>  	case DMA_SLAVE_CONFIG:
> @@ -1059,11 +1056,10 @@ static int fsl_dma_device_control(struct dma_chan *dchan,
>  static void fsl_dma_memcpy_issue_pending(struct dma_chan *dchan)
>  {
>  	struct fsldma_chan *chan = to_fsl_chan(dchan);
> -	unsigned long flags;
> 
> -	spin_lock_irqsave(&chan->desc_lock, flags);
> +	spin_lock_bh(&chan->desc_lock);
>  	fsl_chan_xfer_ld_queue(chan);
> -	spin_unlock_irqrestore(&chan->desc_lock, flags);
> +	spin_unlock_bh(&chan->desc_lock);
>  }
> 
>  /**
> @@ -1076,15 +1072,14 @@ static enum dma_status fsl_tx_status(struct dma_chan *dchan,
>  {
>  	struct fsldma_chan *chan = to_fsl_chan(dchan);
>  	enum dma_status ret;
> -	unsigned long flags;
> 
>  	ret = dma_cookie_status(dchan, cookie, txstate);
>  	if (ret == DMA_SUCCESS)
>  		return ret;
> 
> -	spin_lock_irqsave(&chan->desc_lock, flags);
> +	spin_lock_bh(&chan->desc_lock);
>  	fsldma_cleanup_descriptor(chan);
> -	spin_unlock_irqrestore(&chan->desc_lock, flags);
> +	spin_unlock_bh(&chan->desc_lock);
> 
>  	return dma_cookie_status(dchan, cookie, txstate);
>  }
> @@ -1163,11 +1158,10 @@ static irqreturn_t fsldma_chan_irq(int irq, void *data)
>  static void dma_do_tasklet(unsigned long data)
>  {
>  	struct fsldma_chan *chan = (struct fsldma_chan *)data;
> -	unsigned long flags;
> 
>  	chan_dbg(chan, "tasklet entry\n");
> 
> -	spin_lock_irqsave(&chan->desc_lock, flags);
> +	spin_lock_bh(&chan->desc_lock);
> 
>  	/* the hardware is now idle and ready for more */
>  	chan->idle = true;
> @@ -1175,7 +1169,7 @@ static void dma_do_tasklet(unsigned long data)
>  	/* Run all cleanup for this descriptor */
>  	fsldma_cleanup_descriptor(chan);
> 
> -	spin_unlock_irqrestore(&chan->desc_lock, flags);
> +	spin_unlock_bh(&chan->desc_lock);
> 
>  	chan_dbg(chan, "tasklet exit\n");
>  }
> --
> 1.7.5.1
> 
> 
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