Hi Scott, > -----Original Message----- > From: Scott Jiang [mailto:scott.jiang.linux@xxxxxxxxx] > Sent: Wednesday, September 12, 2012 3:09 PM > To: Bhupesh SHARMA > Cc: linux-media@xxxxxxxxxxxxxxx; Laurent Pinchart; Armando VISCONTI; > Shiraz HASHIM; m.szyprowski@xxxxxxxxxxx; uclinux-dist- > devel@xxxxxxxxxxxxxxxxxxxx > Subject: Re: Using MMAP calls on a video capture device having > underlying NOMMU arch > > > > > Now, I see that the requested videobuffers are correctly allocated > via 'vb2_dma_contig_alloc' > > call (see [3] for reference). But the MMAP call fails in > 'vb2_dma_contig_alloc' function > > in mm/nommu.c (see [4] for reference) when it tries to make the > following check: > > > > if (addr != (pfn << PAGE_SHIFT)) > > return -EINVAL; > > > > I address Scott also, as I see that he has worked on the Blackfin > v4l2 capture driver using > > DMA contiguous method and may have seen this issue (on a NOMMU > system) with a v4l2 application > > performing a MMAP operation. > > > > Any comments on what I could be doing wrong here? > > > > int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, > unsigned long pfn, unsigned long size, pgprot_t prot) > { > if ((addr & PAGE_MASK) != (pfn << PAGE_SHIFT)) > return -EINVAL; > > vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP; > return 0; > } > > This patch seems not in current kernel. Hope it can resolve your > problem. Thanks for your pointer. I already referred to this modification a couple of days ago from the Blackfin ucLinux implementation (http://blackfin.uclinux.org/git/?p=linux-kernel;a=blob;f=mm/nommu.c;h=50dc42ec5f71d56fb418a4adfc3169c2f2e930ce;hb=HEAD) and can now safely say the MMAP works fine for all v4l2 drivers on my NOMMU architecture based SoC as well :) BTW, I was wondering whether a patch for the same is already in the pipe to be included in the latest linux kernel, because this is a really important fix for MMAP IO method to work on NOMMU systems (so probably this patch should also be cc'ed to stable kernel list). Till then I think this discussion can help others who see a similar issue on their NOMMU systems. Regards, Bhupesh -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
