From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: [PATCH V2 6/6] spi/spi-pl022: Request/free DMA channels as and when required. Date: Wed, 10 Aug 2011 11:30:52 +0100 Message-ID: <20110810103052.GI1831@n2100.arm.linux.org.uk> References: <566c0525199f498f04422d4c3b2ddd7466648c20.1312965742.git.viresh.kumar@st.com> <20110810090042.GE1831@n2100.arm.linux.org.uk> <4E424F7B.2000800@st.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Cc: Pratyush ANAND , viresh kumar , Rajeev KUMAR , Bhavna YADAV , Bhupesh SHARMA , Shiraz HASHIM , "Koul, Vinod" , "linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org" , Vipin KUMAR , Armando VISCONTI , Amit VIRDI , Vipul Kumar SAMAR , Deepak SIKRI , "spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org" , Dan Williams , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" To: Jassi Brar Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: spi-devel-general-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: linux-spi.vger.kernel.org On Wed, Aug 10, 2011 at 03:39:28PM +0530, Jassi Brar wrote: > On Wed, Aug 10, 2011 at 2:59 PM, viresh kumar wrote: > > On 08/10/2011 02:30 PM, Russell King - ARM Linux wrote: > >>> > They must be allocated when they are required and must be freed aft= er we are > >>> > done with transfers. So that they can be used by other users. > >> Which DMA engine driver requires this? > >> > > > > dw_dmac.c > > > >> Normally, when we have DMA engine drivers with multiple request signal= s, > >> the slave peripheral side publishes several virtual channels which are > >> claimed by the peripheral drivers. =A0This (amongst other things) allo= ws > >> the peripheral drivers to hold claim to one of the virtual channels > >> all the time that it's required. > > > > If users of DMA expect DMA engine drivers to work this way, then we sho= uld > > have this mentioned clearly in DMA slave documentation. > = > The requirement stems from the fact that most DMACs(esp third party) coul= d be > made to reroute req-signals by the platform, it has not much to do with t= he API. > IMO, all dmac drivers should be implemented that way to be on the safer s= ide. No it isn't. It's to do with how the physical channels are used. ---------------------------------------------------------------------------= --- uberSVN's rich system and user administration capabilities and model = configuration take the hassle out of deploying and managing Subversion and = the tools developers use with it. Learn more about uberSVN and get a free = download at: http://p.sf.net/sfu/wandisco-dev2dev