Vinod Koul <vinod.koul@xxxxxxxxx> writes: > + * DMA_CTRL_REUSE > + - If set, the descriptor can be reused after being completed. It should > + not be freed by provider if this flag is set. > + - The descriptor should be prepared for reuse by invoking > + dmaengine_desc_set_reuse() which will set DMA_CTRL_REUSE. > + - dmaengine_desc_set_reuse() will succeed only when channel support > + reusable descriptor as exhibited by capablities > + - As a consequence, if a device driver wants to skip the dma_map_sg() and > + dma_unmap_sg() in between 2 transfers, because the DMA'd data wasn't used, > + it can resubmit the transfer right after its completion. > + - Descriptor can be freed in few ways > + - Clearing DMA_CTRL_REUSE by invoking dmaengine_desc_clear_reuse() > + and submitting for last txn > + - Explicitly invoking dmaengine_desc_free(), this can succeed only > + when DMA_CTRL_REUSE is already set > + - Terminating the channel Is this last condition mandatory, or can it be transformed into : - Clearing DMA_CTRL_REUSE and terminating the channel The reason I'm asking this is for this kind of scenario : - 4 video buffers are prepared and submitted (ie. 4 txs) - 1st video buffer completes - 2nd video buffer starts, and an error occurs in this 2nd buffer => the driver will terminate the DMA channel to stop the transmission - the driver will wait for the next "start of frame" of the camera sensor - and then it will start 3rd video buffer => in this case, the 3rd video will be reused, even if the channel was terminated Cheers. -- Robert -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
