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

[Liu Qiang-B32616 <B32616@xxxxxxxxxxxxx>]

> -----Original Message-----
> From: Ira W. Snyder [mailto:iws@xxxxxxxxxxxxxxxx]
> Sent: Thursday, August 02, 2012 1:31 AM
> To: Liu Qiang-B32616
> Cc: linux-crypto@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; dan.j.williams@xxxxxxxxx; Vinod Koul; Tabi Timur-
> B04825; herbert@xxxxxxxxxxxxxxxxxxxx; Dan Williams; davem@xxxxxxxxxxxxx
> Subject: Re: [PATCH v5 5/6] fsl-dma: use spin_lock_bh to instead of
> spin_lock_irqsave
> 
> On Wed, Aug 01, 2012 at 04:50:09PM +0800, qiang.liu@xxxxxxxxxxxxx wrote:
> > From: Qiang Liu <qiang.liu@xxxxxxxxxxxxx>
> >
> > - 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.
> """
I will modify the description in v6, please check later.

> 
> Other than that,
> Acked-by: Ira W. Snyder <iws@xxxxxxxxxxxxxxxx>
Thanks.

> 
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Vinod Koul <vinod.koul@xxxxxxxxx>
> > Cc: Li Yang <leoli@xxxxxxxxxxxxx>
> > Cc: Timur Tabi <timur@xxxxxxxxxxxxx>
> > Signed-off-by: Qiang Liu <qiang.liu@xxxxxxxxxxxxx>
> > ---
> >  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
> >
> >
> > _______________________________________________
> > Linuxppc-dev mailing list
> > Linuxppc-dev@xxxxxxxxxxxxxxxx
> > https://lists.ozlabs.org/listinfo/linuxppc-dev


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