> ---------- Original message ----------
> From: Haavard Skinnemoen <haavard.skinnemoen@xxxxxxxxx>
> Date: Jun 26, 2008 3:23 PM
> Subject: [PATCH v4 2/6] dmaengine: Add dma_chan_is_in_use() function
> To: Dan Williams <dan.j.williams@xxxxxxxxx>, Pierre Ossman
> <drzeus-list@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-embedded@xxxxxxxxxxxxxxx,
> kernel@xxxxxxxxxxxxxx, shannon.nelson@xxxxxxxxx, David Brownell
> <david-b@xxxxxxxxxxx>, Haavard Skinnemoen
> <haavard.skinnemoen@xxxxxxxxx>
>
>
> 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 <haavard.skinnemoen@xxxxxxxxx>
> ---
> 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 <maciej.sosnowski@xxxxxxxxx>
Regards,
Maciej
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