Hello Clemens, Takashi, On Fri, May 20, 2011 at 10:17 AM, Takashi Iwai <tiwai@xxxxxxx> wrote: > At Fri, 20 May 2011 08:51:03 +0200, > Clemens Ladisch wrote: >> >> Leon Woestenberg wrote: >> > On Thu, May 19, 2011 at 5:58 PM, Clemens Ladisch <clemens@xxxxxxxxxx> wrote: >> >>> On Thu, May 19, 2011 at 12:14:40AM +0200, Leon Woestenberg wrote: >> >>> > vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); >> >> >> >> So is this an architecture without coherent caches? >> > >> > My aim is to have an architecture independent driver. >> >> Please note that most MMU architectures forbid mapping the same memory >> with different attributes, so you must use pgprot_noncached if and only >> if dma_alloc_coherent actually uses it. Something like the code below. >> >> And I'm not sure if you have to do some additional cache flushes when >> mapping on some architectures. >> >> >> Or would you want to use pgprot_dmacoherent, if available? >> > >> > Hmm, let me check that. >> >> It's available only on ARM and Unicore32. >> >> There's also dma_mmap_coherent(), which does exactly what you want if >> your buffer is physically contiguous, but it's ARM only. >> Takashi tried to implement it for other architectures; I don't know >> what came of it. > > PPC got this recently (thanks to Ben), but still missing in other > areas. > > There was little uncertain issue on MIPS, and it looks difficult to > achieve it on PA-RISC at all. The development was stuck due to lack > of time since then. > Thanks for all the insights, I wasn't aware there were arch-specific calls that already solved the topic issue. Having dma_mmap_coherent() there is good for one or two archs, but how can we built portable drivers if the others arch's are still missing? I assume this call is thus not officially DMA-API (yet)? Clemens showed some pretty amazing preprocessor #if(def)s to cater for the all the different arch's and their mapping/cache-coherency behaviour, but that's not something I would like to put in a driver. How would dma_mmap_coherent() look like on x86? Regards, -- Leon -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
