On Tue, 2009-06-09 at 13:50 +1000, Benjamin Herrenschmidt wrote: > On Sun, 2009-06-07 at 20:06 +0530, Subrata Modak wrote: > > On Sat, 2009-06-06 at 09:36 -0400, Frank Mori Hess wrote: > > > On Saturday 06 June 2009, Greg KH wrote: > > > > Frank and Ian, any thoughts about the vmap call in the > > > > comedi_buf_alloc() call? Why is it using PAGE_KERNEL_NOCACHE, and what > > > > is the prealloc_buf buffer used for? > > > > > > It is a circular buffer used to hold data streaming either to or from a > > > board (for example when producing an analog output waveform). Reads and > > > writes to the device files read/write to the circular buffer, plus a few > > > drivers do dma directly to/from it. I personally don't have a problem > > > with requiring drivers to have their own dma buffers and making them copy > > > data between their private dma buffers and the main circular buffer. I > > > guess the original design wanted to support zero-copy dma. > > > > Great to hear that. How about a patch that solves my build problem on > > PPC64(the problem seems to be existing for long) ? > > In any case, doing PAGE_KERNEL_NOCACHE for DMA memory is incorrect on > many architectures. So at this stage, there's no much option but ifdef I > suspect for now until this is fixed properly. Ok. But, i am not sure whether Greg will agree to this. If, Ok, is the following patch i sent earlier Ok ? http://lkml.org/lkml/2009/6/5/462, Regards-- Subrata > > It does make sense to want to have some memory like that shared between > user space and DMA, though I don't know what the right approach that > works on all archs is at this stage. Worth asking the Alsa guys, I think > they have similar issues :-) > > But doing double buffering might do the trick fine for now. > > Cheers, > Ben. > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
