> On 08.05.2015, at 13:20, Jonathan Bell <jonathan@xxxxxxxxxxxxxxx> wrote: >> > I agree that the interrupt generated would be spurious - in the case where it is not required. > > However if you do && (flags & DMA_PREP_INTERRUPT) then all users of this driver need to explicitly set interrupt flags when doing a scatter-gather transfer. As I understand it, currently the only upstream client of this driver is the I2S driver which only uses cyclic anyway. > > Not requiring an interrupt on completion is a bit of an edge case - the default among other dmaengine drivers appears to be to enable interrupts unconditionally. I have now submitted a patch for spi-bcm2835 to make use of dma, so there is one candidate for this kind of behavior. So please go forward with the merge. Also note that with the spi-HW dma support of the bcm2835 it is necessary to do a RX transfer even if the data is not used (similar for TX). Right now we have to allocate a dummy buffer to run these kind of “one-way” transfers where we need 2 DMA channels. The bcm2835 dma hw supports such dummy-transfer modes via BCM2835_DMA_S_IGNORE and BCM2835_DMA_D_IGNORE. So maybe we can add a “flag” to the dmaengine_prep_slave_sg that will allow such kind of behavior to get implemented? That is not a necessity, but would be a welcome improvement. Tested-by: Martin Sperl <kernel@xxxxxxxxxxxxxxxx> -- 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
