On Wed, Aug 10, 2011 at 4:00 PM, Russell King - ARM Linux <li...@arm.linux.org.uk> wrote: > On Wed, Aug 10, 2011 at 03:39:28PM +0530, Jassi Brar wrote: >> On Wed, Aug 10, 2011 at 2:59 PM, viresh kumar <viresh.ku...@st.com> 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 after >> >>> > 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 signals, >> >> the slave peripheral side publishes several virtual channels which are >> >> claimed by the peripheral drivers. This (amongst other things) allows >> >> 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 should >> > have this mentioned clearly in DMA slave documentation. >> >> The requirement stems from the fact that most DMACs(esp third party) could be >> made to reroute req-signals by the platform, it has not much to do with the >> API. >> IMO, all dmac drivers should be implemented that way to be on the safer side. > > No it isn't. It's to do with how the physical channels are used. IMO, a dmac driver developer sees only two aspects - "virtual channel" at frontend and "ReqSig/PhyChan" management at the backend. While ReqSig and Physical Channels are different h/w entities, the driver developer usually works having tied them together.
For ex, PL330 has 8 physical channels(ARM calls them threads) and 32 peripheral interfaces(ReqSig), where as the dmac driver freely allocates 32 virtual channels and keeps in mind that only 8 peripheral interfaces can be active at any time. So I am unable to see how I said something different that you do. ------------------------------------------------------------------------------ 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 _______________________________________________ spi-devel-general mailing list spi-devel-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/spi-devel-general
