From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH V2] dma: tegra: register as an OF DMA controller Date: Wed, 04 Dec 2013 10:09:39 -0700 Message-ID: <529F61D3.3030104@wwwdotorg.org> References: <1385416416-3536-1-git-send-email-swarren@wwwdotorg.org> <201311292208.26215.arnd@arndb.de> <529E1A49.6050808@wwwdotorg.org> <201312040222.03604.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <201312040222.03604.arnd-r2nGTMty4D4@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Arnd Bergmann Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Dan Williams , Vinod Koul , Stephen Warren , pdeschrijver-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, Lars-Peter Clausen List-Id: linux-tegra@vger.kernel.org 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.