Re: [PATCH] dmaengine: pl330: Set residue in tx_status callback

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Dec 03, 2014 at 01:21:37PM +0530, Jassi Brar wrote:
> because the reasoning above seems incorrect considering the following
> documentation...
> 
> Documentation/crypto/async-tx-api.txt says
                       ^^^^^^^^^^^^

async-tx-api is not the DMA slave API.

>   " .... 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(). ...."
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^

DMA slave users do not call this function.  This documentation is not
relevant for DMA slave.

> include/linux/dmaengine.h says
>   dma_async_tx_descriptor.tx_submit(): set the prepared descriptor(s)
> to be executed by the engine

It doesn't say when.

> so theoretically a driver, not starting transfer until
> issue_pending(), is "broken".

It isn't.  DMA slave engine implementations have been needing the
issue_pending() call since their dawn, so it's something that they've
always needed.

> At best the patch@04abf5daf7d makes the driver slightly more
> complicated and the reason behind confusion such as in this thread.

That may be, and yes, it _might_ be worth discussing whether this should
be relaxed or not, but that should be done as a proposal, not trying to
hide it as a bug fix.  It isn't.

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