Even with the introduced vchan_synchronize() we can face race when
terminating a cyclic transfer.

If the terminate_all is called after the interrupt handler called
vchan_cyclic_callback(), but before the vchan_complete tasklet is called:
vc->cyclic is set to the cyclic descriptor, but the descriptor itself was
freed up in the driver's terminate_all() callback.
When the vhan_complete() is executed it will try to fetch the vc->cyclic
vdesc, but the pointer is pointing now to uninitialized memory leading to
(hard to reproduce) kernel crash.

In order to fix this, drivers should:
- call vchan_terminate_vdesc() from their terminate_all callback instead
calling their free_desc function to free up the descriptor.
- implement device_synchronize callback and call vchan_synchronize().

This way we can make sure that the descriptor is only going to be freed up
after the vchan_callback was executed in a safe manner.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

The vchan_vdesc_fini() can be used to free or reuse a given descriptor
after it has been marked as completed.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

We get 2 warnings when building kernel with W=1:
drivers/dma/virt-dma.c:22:14: warning: no previous prototype for 'vchan_tx_submit' [-Wmissing-prototypes]
drivers/dma/virt-dma.c:52:5: warning: no previous prototype for 'vchan_tx_desc_free' [-Wmissing-prototypes]

In fact, these two functions are incorrectly declared in a function.

So this patch moves function declarations out of this function.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

The combo of list_empty() check and return list_first_entry()
can be replaced with list_first_entry_or_null().

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

This patch attempts to enhance the case of a transfer submitted multiple
times, and where the cost of creating the descriptors chain is not
negligible.

This happens with big video buffers (several megabytes, ie. several
thousands of linked descriptors in one scatter-gather list). In these
cases, a video driver would want to do :
 - tx = dmaengine_prep_slave_sg()
 - dma_engine_submit(tx);
 - dma_async_issue_pending()
 - wait for video completion
 - read video data (or not, skipping a frame is also possible)
 - dma_engine_submit(tx)
   => here, the descriptors chain recalculation will take time
   => the dma coherent allocation over and over might create holes in
      the dma pool, which is counter-productive.
 - dma_async_issue_pending()
 - etc ...

In order to cope with this case, virt-dma is modified to prevent freeing
the descriptors upon completion if DMA_CTRL_REUSE flag is set in the
transfer.

This patch is a respin of the former DMA_CTRL_ACK approach, which was
reverted due to a regression in audio drivers.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

Add a synchronize helper function for the virt-dma library. The function
makes sure that any scheduled descriptor complete callbacks have finished
running before the function returns.

This needs to be called by drivers using virt-dma in their
device_synchronize() callback. Depending on the driver additional
operations might be necessary in addition to calling vchan_synchronize() to
ensure proper synchronization.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

In kernel-doc annotations parameters need to start with a @ for them to be
properly recognized. Add those where missing for virt-dma.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

This reverts commit b9855f03d560d351e95301b9de0bc3cad3b31fe9.
The patch break existing DMA usage case. For example, audio SOC
dmaengine never release channel and cause virt-dma to cache too
much memory in descriptor to exhaust system memory.

Signed-off-by: Vinod Koul <vinod.koul@intel.com>

This patch attempts to enhance the case of a transfer submitted multiple
times, and where the cost of creating the descriptors chain is not
negligible.

This happens with big video buffers (several megabytes, ie. several
thousands of linked descriptors in one scatter-gather list). In these
cases, a video driver would want to do :
 - tx = dmaengine_prep_slave_sg()
 - dma_engine_submit(tx);
 - dma_async_issue_pending()
 - wait for video completion
 - read video data (or not, skipping a frame is also possible)
 - dma_engine_submit(tx)
   => here, the descriptors chain recalculation will take time
   => the dma coherent allocation over and over might create holes in
      the dma pool, which is counter-productive.
 - dma_async_issue_pending()
 - etc ...

In order to cope with this case, virt-dma is modified to prevent freeing
the descriptors upon completion if DMA_CTRL_ACK flag is set in the
transfer.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>