> ---------- Original message ---------- > From: Haavard Skinnemoen <[EMAIL PROTECTED]> > Date: Jun 26, 2008 3:23 PM > Subject: [PATCH v4 2/6] dmaengine: Add dma_chan_is_in_use() function > To: Dan Williams <[EMAIL PROTECTED]>, Pierre Ossman > <[EMAIL PROTECTED]> > Cc: [EMAIL PROTECTED], [email protected], > [EMAIL PROTECTED], [EMAIL PROTECTED], David Brownell > <[EMAIL PROTECTED]>, Haavard Skinnemoen > <[EMAIL PROTECTED]> > > > This moves the code checking if a DMA channel is in use from > show_in_use() into an inline helper function, dma_is_in_use(). DMA > controllers can use this in order to give clients exclusive access to > channels (usually necessary when setting up slave DMA.) > > I have to admit that I don't really understand the channel refcounting > logic at all... dma_chan_get() simply increments a per-cpu value. How > can we be sure that whatever CPU calls dma_chan_is_in_use() sees the > same value? > > Signed-off-by: Haavard Skinnemoen <[EMAIL PROTECTED]> > --- > drivers/dma/dmaengine.c | 12 +----------- > include/linux/dmaengine.h | 17 +++++++++++++++++ > 2 files changed, 18 insertions(+), 11 deletions(-) > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c > index a57c337..ad8d811 100644 > --- a/drivers/dma/dmaengine.c > +++ b/drivers/dma/dmaengine.c > @@ -105,17 +105,7 @@ static ssize_t show_bytes_transferred(struct > device *dev, struct device_attribut > static ssize_t show_in_use(struct device *dev, struct > device_attribute *attr, char *buf) > { > struct dma_chan *chan = to_dma_chan(dev); > - int in_use = 0; > - > - if (unlikely(chan->slow_ref) && > - atomic_read(&chan->refcount.refcount) > 1) > - in_use = 1; > - else { > - if (local_read(&(per_cpu_ptr(chan->local, > - get_cpu())->refcount)) > 0) > - in_use = 1; > - put_cpu(); > - } > + int in_use = dma_chan_is_in_use(chan); > > return sprintf(buf, "%d\n", in_use); > } > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h > index cffb95f..4b602d3 100644 > --- a/include/linux/dmaengine.h > +++ b/include/linux/dmaengine.h > @@ -180,6 +180,23 @@ static inline void dma_chan_put(struct dma_chan *chan) > } > } > > +static inline bool dma_chan_is_in_use(struct dma_chan *chan) > +{ > + bool in_use = false; > + > + if (unlikely(chan->slow_ref) && > + atomic_read(&chan->refcount.refcount) > 1) > + in_use = true; > + else { > + if (local_read(&(per_cpu_ptr(chan->local, > + get_cpu())->refcount)) > 0) > + in_use = true; > + put_cpu(); > + } > + > + return in_use; > +} > + > /* > * typedef dma_event_callback - function pointer to a DMA event callback > * For each channel added to the system this routine is called for each > client. -- > 1.5.5.4
Acked-by: Maciej Sosnowski <[EMAIL PROTECTED]> Regards, Maciej -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
