From mboxrd@z Thu Jan 1 00:00:00 1970 From: mans@mansr.com (=?iso-8859-1?Q?M=E5ns_Rullg=E5rd?=) Date: Thu, 08 Dec 2016 16:46:15 +0000 Subject: Tearing down DMA transfer setup after DMA client has finished In-Reply-To: <20161208154018.GD6408@localhost> (Vinod Koul's message of "Thu, 8 Dec 2016 21:10:18 +0530") References: <20161125045549.GC2698@localhost> <092f44ee-4560-be17-25f7-00948dba3cfa@free.fr> <20fc9020-7278-bc2f-2a8d-43aff5cabff8@free.fr> <20161206051222.GQ6408@localhost> <5846B237.8060409@free.fr> <20161207164341.GX6408@localhost> <20161208103921.GC6408@localhost> <20161208154018.GD6408@localhost> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Vinod Koul writes: > On Thu, Dec 08, 2016 at 11:44:53AM +0000, M?ns Rullg?rd wrote: >> Vinod Koul writes: >> >> > On Wed, Dec 07, 2016 at 04:45:58PM +0000, M?ns Rullg?rd wrote: >> >> Vinod Koul writes: >> >> >> >> > On Tue, Dec 06, 2016 at 01:14:20PM +0000, M?ns Rullg?rd wrote: >> >> >> >> >> >> That's not going to work very well. Device drivers typically request >> >> >> dma channels in their probe functions or when the device is opened. >> >> >> This means that reserving one of the few channels there will inevitably >> >> >> make some other device fail to operate. >> >> > >> >> > No that doesnt make sense at all, you should get a channel only when you >> >> > want to use it and not in probe! >> >> >> >> Tell that to just about every single driver ever written. >> > >> > Not really, few do yes which is wrong but not _all_ do that. >> >> Every driver I ever looked at does. Name one you consider "correct." > > That only tells me you haven't looked enough and want to rant! > > FWIW look at ALSA-dmaengine lib, thereby every audio driver that uses it. I > could find other examples and go on and on, but that's besides the point and > looks like you don't want to listen to people telling you something.. ALSA is a particularly poor example. ALSA drivers request a dma channel at some point between the device being opened and playback (or capture) starting. They then set up a cyclic transfer that runs continuously until playback is stopped. It's a completely different model of operation than we're talking about here. -- M?ns Rullg?rd