On Tue, Jun 9, 2009 at 20:34, Subrata Modak<subrata@xxxxxxxxxxxxxxxxxx> wrote: > 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, Your patch helps powerpc only. Compilation is still broken on most other architectures. >> 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. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- 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
