On 12/04/2013 06:09 PM, Stephen Warren wrote: > 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. It's not like this is a hot path or that the mask checking is expensive. I'd keep it as it is for the sake of not having the same code twice. And the DMA_PRIVATE check should probably also stay. - Lars -- 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
