On 2016-02-26 13:25, Russell King - ARM Linux wrote: >>> Your original commit adding the original hack that you're now removing >>> above says that this is to support polled operation: I'm not aware of >>> DMA engine supporting such a mode. DMA_PREP_INTERRUPT is a mechanism >>> where requests can be queued without an interrupt to allow batching. >> >> Also it is used to suppress DMA interrupts during audio playback for example. >> In this case we will run w/o interrupts and the position is polled. >> >>> See the raid5/async_tx code, which queues a set of operations without >>> DMA_PREP_INTERRUPT, with the final operation with DMA_PREP_INTERRUPT >>> set. >> >> We only allow the interrupts to be disabled in cyclic or memcpy mode. With >> slave_sg we have interrupts as it is needed to move to the next SG. >> >>> As the driver is reliant on interrupts to move to the next transfer, >>> the patch which causes DMA_PREP_INTERRUPT to influence whether >>> interrupts are sent is actually buggy, and will prevent several >>> queued DMA operations to fail. >> >> Yes, the omap-dma only allows the interrupts to be actually disabled when it >> is save to do so. slave_sg can not work w/o interrupts so there we don't >> disable them. > > I get the impression that you haven't taken in what I've said, because > each fragment of your reply is just repeating what the previous fragment > said. Sorry about that. I got it. > Let me state that I don't believe you need any hacks here, and this patch > is not necessary: the final operation in a set of chained memcpy()s should > have DMA_PREP_INTERRUPT set. calling the omap_dma_callback() from the tx_status() was a bad idea, this is why I'm fixing it. As for the DMA_PREP_INTERRUPT not enabling interrupt was introduced by: 4ce98c0a20bef (dmaengine: omap-dma: Add support for memcpy) While we do not have users submitting multiple descriptors I agree that this is a possibility and the driver should not fail in such a case. I can send a followup patch to fix the omap_dma_prep_dma_memcpy() -- Péter -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
