Re: Problems with dma_mmap_writecombine on mach-pxa

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Thu, Feb 17, 2005 at 06:51:49PM +0100, Frank Buss wrote:
> I'm trying to use the pxafb driver on mach-pxa, but I can't mmap the
> framebuffer memory. I can access it from the driver, filling the entire
> screen, but when I access the pointer returned from mmap from a user space
> program, the following two things happens:
> 
> - the vm_pgoff is ignored and I get the start of the internal buffer, which
> caused writing to the palette and DMA descriptors
> 
> - when I change the location of the framebuffer to the start of the internal
> buffer, I can write to the screen, but only to the first 4 k; any write
> after this address is ignored, but no segfault is generated.
> 
> Any ideas what I can do to find the reason? I don't think that it is a
> kernel bug, but perhaps a wrong configuration for my platform.

Please try this (and revert your changes):

===== arch/arm/mm/consistent.c 1.27 vs edited =====
--- 1.27/arch/arm/mm/consistent.c	2005-01-21 05:02:14 +00:00
+++ edited/arch/arm/mm/consistent.c	2005-02-17 18:11:50 +00:00
@@ -284,13 +284,15 @@
 	spin_unlock_irqrestore(&consistent_lock, flags);
 
 	if (c) {
+		unsigned long off = vma->vm_pgoff;
+
 		kern_size = (c->vm_end - c->vm_start) >> PAGE_SHIFT;
 
-		if (vma->vm_pgoff < kern_size &&
-		    user_size <= (kern_size - vma->vm_pgoff)) {
+		if (off < kern_size &&
+		    user_size <= (kern_size - off)) {
 			vma->vm_flags |= VM_RESERVED;
 			ret = remap_pfn_range(vma, vma->vm_start,
-					      page_to_pfn(c->vm_pages),
+					      page_to_pfn(c->vm_pages) + off,
 					      user_size, vma->vm_page_prot);
 		}
 	}


-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core