Subject: Bigphysarea vs. kernel 2.4.32 and PPC405GPr

From: Stephen Williams <[email-masked]>
Date: Fri, 12 May 2006 16:31:09 -0700

I'm trying to use the bigphysarea patch to help me allocate big
physical chunks of memory for use by some custom embedded devices.
I've applied the bigphysarea-2.4.20 patch and built, no trouble,
and I've got it to config for my PPC. I can see at boot time that
the bigphysarea is getting its pages.

I'm trying to use a mmap call to the driver to map a chunk of this
memory into the process. The mmap for the driver has this:

      pgprot_val(vma->vm_page_prot) |= _PAGE_NO_CACHE;
      vma->vm_flags |= VM_RESERVED;

      npages = (vma->vm_end - vma->vm_start) / PAGE_SIZE;
      heap_map_base = bigphysarea_alloc_pages(npages, 1, GFP_KERNEL);

      printk("XXXX Map base=%p, %ld pages\n", heap_map_base, npages);

      rc = remap_page_range(vma->vm_start,
			    (unsigned long)heap_map_base,
			    npages*PAGE_SIZE,
			    vma->vm_page_prot);

The mmap returns without an error, but any access to the mapped
region gets me an immediate "Oops: machine check, sig: 7". I don't
see it. Where is the stupid mistake that I'm invariably making?

-- 
Steve Williams                "The woods are lovely, dark and deep.
steve at icarus.com           But I have promises to keep,
http://www.icarus.com         and lines to code before I sleep,
http://www.picturel.com       And lines to code before I sleep."