From: Andrew Morton <akpm@linux-foundation.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
maciej.sosnowski@intel.com, hskinnemoen@atmel.com,
g.liakhovetski@gmx.de, nicolas.ferre@atmel.com
Subject: Re: [PATCH 02/13] dmaengine: remove dependency on async_tx
Date: Fri, 14 Nov 2008 22:02:14 -0800 [thread overview]
Message-ID: <20081114220214.4168ae1b.akpm@linux-foundation.org> (raw)
In-Reply-To: <20081114213426.32354.75721.stgit@dwillia2-linux.ch.intel.com>
On Fri, 14 Nov 2008 14:34:27 -0700 Dan Williams <dan.j.williams@intel.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.
next prev parent reply other threads:[~2008-11-15 6:02 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-14 21:34 [PATCH 00/13] dmaengine redux Dan Williams
2008-11-14 21:34 ` [PATCH 01/13] async_tx, dmaengine: document channel allocation and api rework Dan Williams
2008-11-14 21:34 ` [PATCH 02/13] dmaengine: remove dependency on async_tx Dan Williams
2008-11-15 6:02 ` Andrew Morton [this message]
2008-11-17 23:44 ` Dan Williams
2008-11-14 21:34 ` [PATCH 03/13] dmaengine: up-level reference counting to the module level Dan Williams
2008-11-15 6:08 ` Andrew Morton
2008-11-18 3:42 ` Dan Williams
2008-12-04 16:56 ` Guennadi Liakhovetski
2008-12-04 18:51 ` Dan Williams
2008-12-04 19:28 ` Guennadi Liakhovetski
2008-12-08 22:39 ` Dan Williams
2008-12-12 14:28 ` Sosnowski, Maciej
2008-12-15 22:12 ` Dan Williams
2008-12-18 14:26 ` Sosnowski, Maciej
2008-11-14 21:34 ` [PATCH 04/13] dmaengine: centralize channel allocation, introduce dma_find_channel Dan Williams
2008-11-15 6:14 ` Andrew Morton
2008-11-18 5:59 ` Dan Williams
2008-11-14 21:34 ` [PATCH 05/13] dmaengine: provide a common 'issue_pending_all' implementation Dan Williams
2008-11-14 21:34 ` [PATCH 06/13] net_dma: convert to dma_find_channel Dan Williams
2008-11-14 21:34 ` [PATCH 07/13] dmaengine: introduce dma_request_channel and private channels Dan Williams
2008-12-02 15:52 ` Guennadi Liakhovetski
2008-12-02 17:16 ` Dan Williams
2008-12-02 17:27 ` Guennadi Liakhovetski
2008-12-02 19:10 ` Dan Williams
2008-12-02 21:28 ` Guennadi Liakhovetski
2009-01-30 17:03 ` Atsushi Nemoto
2009-01-30 23:13 ` Dan Williams
2009-01-30 23:27 ` Guennadi Liakhovetski
2009-01-31 12:18 ` Atsushi Nemoto
2008-12-02 17:26 ` Nicolas Ferre
2008-12-12 14:29 ` Sosnowski, Maciej
2008-12-15 23:55 ` Dan Williams
2008-12-18 14:33 ` Sosnowski, Maciej
2008-12-18 17:27 ` Dan Williams
2009-02-06 16:58 ` Atsushi Nemoto
2008-11-14 21:34 ` [PATCH 08/13] dmatest: convert to dma_request_channel Dan Williams
2008-11-15 6:17 ` Andrew Morton
2008-11-18 18:24 ` Dan Williams
2008-11-18 20:58 ` Andrew Morton
2008-11-18 22:19 ` Dan Williams
2008-11-14 21:35 ` [PATCH 09/13] atmel-mci: convert to dma_request_channel and down-level dma_slave Dan Williams
2009-01-30 16:40 ` Atsushi Nemoto
2009-01-30 23:02 ` Dan Williams
2008-11-14 21:35 ` [PATCH 10/13] dmaengine: replace dma_async_client_register with dmaengine_get Dan Williams
2008-11-14 21:35 ` [PATCH 11/13] dmaengine: kill struct dma_client and supporting infrastructure Dan Williams
2008-12-12 14:29 ` Sosnowski, Maciej
2008-12-16 0:09 ` Dan Williams
2008-12-18 14:34 ` Sosnowski, Maciej
2008-11-14 21:35 ` [PATCH 12/13] dmaengine: remove 'bigref' infrastructure Dan Williams
2008-11-14 21:35 ` [PATCH 13/13] dmaengine: kill enum dma_state_client Dan Williams
2008-12-12 14:27 ` [PATCH 00/13] dmaengine redux Sosnowski, Maciej
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