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. 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
