On 2016-02-26 14:45, Peter Ujfalusi wrote: > 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. The reason that we need to be able to determine if the channel is done with the copy by polling the tx_status is: we need to read and write tiler registers with DMA on dra7 as per one ERRATA document. This read/write can be executed in interrupt context so we can not rely on DMA callback to be notified about the completion of the read/write. > 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() With the updated patch based on your comments I can fix the polling in the tx_status callback and with a separate patch I can address your concern regarding to multiple transfers queued with only the last one having DMA_PREP_INTERRUPT (and callback provided). -- Péter -- 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
