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Date: Fri, 14 Nov 2008 22:02:14 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Dan Williams <dan.j.williams@...el.com> Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, maciej.sosnowski@...el.com, hskinnemoen@...el.com, g.liakhovetski@....de, nicolas.ferre@...el.com Subject: Re: [PATCH 02/13] dmaengine: remove dependency on async_tx On Fri, 14 Nov 2008 14:34:27 -0700 Dan Williams <dan.j.williams@...el.com> wrote: > async_tx.ko is a consumer of dma channels. A circular dependency arises > if modules in drivers/dma rely on common code in async_tx.ko. It > prevents either module from being unloaded. > > Move dma_wait_for_async_tx and async_tx_run_dependencies to dmaeninge.o > where they should have been from the beginning. > > > ... > > --- a/drivers/dma/dmaengine.c > +++ b/drivers/dma/dmaengine.c > @@ -623,6 +623,81 @@ void dma_async_tx_descriptor_init(struct dma_async_tx_descriptor *tx, > } > EXPORT_SYMBOL(dma_async_tx_descriptor_init); > > +/* dma_wait_for_async_tx - spin wait for a transcation to complete yuo cnat sepll > + * @tx: transaction to wait on > + */ > +enum dma_status > +dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx) > +{ > + enum dma_status status; > + struct dma_async_tx_descriptor *iter; > + struct dma_async_tx_descriptor *parent; > + > + if (!tx) > + return DMA_SUCCESS; > + > + /* poll through the dependency chain, return when tx is complete */ > + do { > + iter = tx; > + > + /* find the root of the unsubmitted dependency chain */ > + do { > + parent = iter->parent; > + if (!parent) > + break; > + else > + iter = parent; > + } while (parent); > + > + /* there is a small window for ->parent == NULL and > + * ->cookie == -EBUSY > + */ > + while (iter->cookie == -EBUSY) > + cpu_relax(); > + > + status = dma_sync_wait(iter->chan, iter->cookie); > + } while (status == DMA_IN_PROGRESS || (iter != tx)); > + > + return status; > +} > +EXPORT_SYMBOL_GPL(dma_wait_for_async_tx); hm, strange. The unlocked list walk assumes that this thread of control has exclusive access to *tx (somehow??), but this thread of control doesn't end up freeing *tx. I guess the caller does that. > +/* dma_run_dependencies - helper routine for dma drivers to process > + * (start) dependent operations on their target channel > + * @tx: transaction with dependencies > + */ > +void dma_run_dependencies(struct dma_async_tx_descriptor *tx) > +{ > + struct dma_async_tx_descriptor *dep = tx->next; > + struct dma_async_tx_descriptor *dep_next; > + struct dma_chan *chan; > + > + if (!dep) > + return; > + > + chan = dep->chan; > + > + /* keep submitting up until a channel switch is detected > + * in that case we will be called again as a result of > + * processing the interrupt from async_tx_channel_switch > + */ > + for (; dep; dep = dep_next) { > + spin_lock_bh(&dep->lock); > + dep->parent = NULL; > + dep_next = dep->next; > + if (dep_next && dep_next->chan == chan) > + dep->next = NULL; /* ->next will be submitted */ > + else > + dep_next = NULL; /* submit current dep and terminate */ > + spin_unlock_bh(&dep->lock); > + > + dep->tx_submit(dep); > + } > + > + chan->device->device_issue_pending(chan); > +} > +EXPORT_SYMBOL_GPL(dma_run_dependencies); Now there's a lock. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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