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>
This reverts commit b9855f03d5.
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>
Add support for cyclic DMA's periodic callbacks. Drivers are expected
to call vchan_cyclic_callback() when a period has completed, which will
schedule the tasklet to make the callback into the driver.
As callbacks are made from tasklet context, it is important to realise
that we don't guarantee a callback for each completed period, but for
N completed periods where N may be greater than one.
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Add a function to find a descriptor within the depths of the
virtualized DMA channel support. Needed for tx_status functionality.
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Split the virtual slave channel DMA support from the sa11x0 driver so
this code can be shared with other slave DMA engine drivers.
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Robert Jarzmik