Messages in this thread | | | Date | Thu, 28 Apr 2011 15:46:06 +0900 | Subject | Re: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1 | From | FUJITA Tomonori <> |
| |
On Thu, 28 Apr 2011 08:40:08 +0200 Arnd Bergmann <arnd@arndb.de> wrote:
> On Wednesday 27 April 2011 23:37:51 Benjamin Herrenschmidt wrote: > > On Wed, 2011-04-27 at 08:35 +0100, Russell King - ARM Linux wrote: > > > On Thu, Apr 21, 2011 at 09:29:16PM +0200, Arnd Bergmann wrote: > > > > 2. Implement dma_alloc_noncoherent on ARM. Marek pointed out > > > > that this is needed, and it currently is not implemented, with > > > > an outdated comment explaining why it used to not be possible > > > > to do it. > > > > > > dma_alloc_noncoherent is an entirely pointless API afaics. > > > > I was about to ask what the point is ... (what is the expected > > semantic ? Memory that is reachable but not necessarily cache > > coherent ?) > > Drivers use this when they explicitly want to manage the caching > themselves.
Not "want to manage". The API is for drivers that "have to" manage the cache because of architectures that can't allocate coherent memory.
> I think this is most interesting on big NUMA systems, > where you really want to use fast (local cached) memory and > then flush it explicitly to do dma. Very few drivers use this:
| |