On Feb 13, 2008 2:06 PM, Haavard Skinnemoen <[EMAIL PROTECTED]> wrote: > On Wed, 13 Feb 2008 12:11:58 -0700 > "Dan Williams" <[EMAIL PROTECTED]> wrote: > > > > + desc = chan->device->device_prep_slave(chan, > > > + sg_dma_address(sg), direction, > > > + DMA_SLAVE_WIDTH_32BIT, > > > + sg_dma_len(sg), dma_flags); > > > + desc->txd.callback = NULL; > > > + list_add_tail(&desc->client_node, > > > + &host->dma.data_descs); > > > + } > > > > Need to handle device_prep_slave returning NULL? > > You're right, we definitely need to handle that. Which probably means > we need to prepare an interrupt descriptor first that we can throw in > when we're unable to obtain more descriptors, and submit the rest from > the callback. > > Except we're not allowed to submit anything from the callback. Ouch. > > How can we solve that? Set up a work queue and submit it from there? > Trigger a different tasklet? > > In any case, I guess I need to implement support for interrupt > descriptors in the dw_dmac driver. >
Well, the other two possibilities are: 1/ Spin/sleep until a descriptor shows up 2/ Fall back to PIO for a few transfers Descriptor availability is improved if the code interleaves allocation and submission. Currently it looks like we wait until all descriptors for the scatterlist are allocated before we start submitting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
