On 12/03/2013 06:22 PM, Arnd Bergmann wrote: > On Tuesday 03 December 2013, Stephen Warren wrote: >> On 11/29/2013 02:08 PM, Arnd Bergmann wrote: > >>> Can you try coming up with a different method to achieve the same >>> where you use a different helper from the driver specific xlate >>> function that does not require a callback? >>> >>> I think dma_get_slave_channel is great if you have one channel per >>> request line and you can directly look up the channel from the >>> DT data, but it is not good if you have pick a channel and work >>> around the race. >> >> Hmm. Can you take a look at "[PATCH V4] dma: add >> dma_get_any_slave_channel(), for use in of_xlate()" at the link below. >> It still implements this via xlate, but I don't see any benefit in >> making drivers use a different API to request slave channels based on >> how the DMA controller works. >> >> http://lkml.org/lkml/2013/11/26/408 > > Yes, I think that is good. I can think of a few variations of that > that I would prefer slightly over your code, but it's essentially > what I had in mind and I'm fine with that version getting merged > as well. Here are my ideas for further improvements, I'll leave > it up to you and the dmaengine maintainers to decide what to do > about them: > > * Rather than calling private_candidate(), open-code the part you > need and remove the pointless dma_cap_mask comparison: > > err = -EBUSY; > list_for_each_entry(chan, &dev->channels, device_node) { > if (!chan->client_count) { > err = dma_chan_get(chan); > break; > } > } Lars-Peter had specifically suggested to call private_candidate(). Lars, what do you think about open-coding this? Arnd's suggestion would skip the DMA_PRIVATE checking that private_candidate() does, and I'm not sure what the implications of that would be. > * Merge the new function with dma_get_slave_channel(). They really > do different things, but I think it still makes sense as an API > to require to always pass the dma_device pointer, and drivers > that want to get an arbitrary channel can just pass NULL as the > channel pointer. I suppose one could do that, although the two operations seem pretty semantically different to me, such that merging them doesn't seem correct. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
