[PATCH] dma: pl330: revert commit 04abf5daf7d

Vinod Koul vinod.koul at intel.com
Fri Dec 5 07:03:02 PST 2014

On Fri, Dec 05, 2014 at 02:38:59PM +0100, Lars-Peter Clausen wrote:
> On 12/05/2014 02:14 PM, Jassi Brar wrote:
> > From Documentation/crypto/async-tx-api.txt
> >   "... Once a driver-specific threshold is met the driver
> >automatically issues pending operations.  An application can force
> >this event by calling async_tx_issue_pending_all() ..."
> >  That is, the DMA controller drivers may buffer transfer requests
> >for optimization. However it is perfectly legal to start dma as soon
> >as the user calls .tx_submit() on the descriptor, as the documentation
> >specifies in include/linux/dmaengine.h
Noooo, submit does not mean that as all

> It's not according to what is in the DMAengine documentation
> (Documentation/dmaengine.txt) and what we have been telling people
> for the last couple of years.
> There are supposed to be two different queues one for pending
> descriptors and one for active descriptors. submit() adds a
> descriptor to the pending list and issue_pending() moves all
> descriptors from the pending list to the active list. Especially the
> driver must not automatically start transferring a descriptor after
> it has been submitted but before issue_pending() has been called.

to quote the Documentation:

       + tx_submit:	A pointer to a function you have to implement,
			that is supposed to push the current
			transaction descriptor to a pending queue, waiting
			for issue_pending to be called.
   * device_issue_pending
     - Takes the first transaction descriptor in the pending queue,
       and starts the transfer. Whenever that transfer is done, it
       should move to the next transaction in the list.
     - This function can be called in an interrupt context

Pls see Documentation/dmaengine/provider.txt in dmaengine-next


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