Messages in this thread Patch in this message | | | From | Haavard Skinnemoen <> | Subject | [RFC v3 3/7] dmaengine: Add dma_chan_is_in_use() function | Date | Tue, 12 Feb 2008 17:43:54 +0100 |
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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 <hskinnemoen@atmel.com> --- 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 9d11f06..3076d80 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 9cd7ed9..5d9a3a2 100644 --- a/include/linux/dmaengine.h +++ b/include/linux/dmaengine.h @@ -175,6 +175,23 @@ 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. -- 1.5.3.8
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