Re: [PATCH 1/9] [I/OAT] DMA memcpy subsystem

[Andrew Morton]

Chris Leech <christopher.leech@xxxxxxxxx> wrote:
>
> +/**
>  + * dma_client_chan_free - release a DMA channel
>  + * @chan: &dma_chan
>  + */
>  +void dma_chan_cleanup(struct kref *kref)
>  +{
>  +	struct dma_chan *chan = container_of(kref, struct dma_chan, refcount);
>  +	chan->device->device_free_chan_resources(chan);
>  +	chan->client = NULL;
>  +	kref_put(&chan->device->refcount, dma_async_device_cleanup);
>  +}
>  +
>  +static void dma_chan_free_rcu(struct rcu_head *rcu)
>  +{
>  +	struct dma_chan *chan = container_of(rcu, struct dma_chan, rcu);
>  +	int bias = 0x7FFFFFFF;
>  +	int i;
>  +	for_each_cpu(i)
>  +		bias -= local_read(&per_cpu_ptr(chan->local, i)->refcount);
>  +	atomic_sub(bias, &chan->refcount.refcount);
>  +	kref_put(&chan->refcount, dma_chan_cleanup);
>  +}
>  +
>  +static void dma_client_chan_free(struct dma_chan *chan)
>  +{
>  +	atomic_add(0x7FFFFFFF, &chan->refcount.refcount);
>  +	chan->slow_ref = 1;
>  +	call_rcu(&chan->rcu, dma_chan_free_rcu);
>  +}

A comment describing this `bias' magic would be nice.
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