Re: Call to mmap in ALSA lib 1.0.13 fails in src/pcm/pcm_mmap.c line 367

[David Cullen <david.cullen@teligy.com>]

Dear Mr. Iwai,

Takashi Iwai wrote:
> The implementation depends pretty much on the architecture.
> (Also, dma_mmap() is no global function but specific only for ARM.)
> Since the vm_region struct is different between ppc and arm (the page
> pointer is missing in ppc version), it cannot be copied as it is.
> 
> A simple (but totally untested) version would be like below:
> 
> int dma_mmap_coherent(struct device *dev,
> 		struct vm_area_struct *vma, void *cpu_addr,
> 		dma_addr_t dma_addr, size_t size)
> {
> 	unsigned long pfn;
> 
> 	pfn = page_to_pfn(virt_to_page(bus_to_virt(dma_addr)));
> 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> 	return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
> 				vma->vm_end - vma->vm_start,
> 				vma->vm_pgprot);
> }
> 
> (This might not work for some ppc models, though...)
> 
> Then either add .mmap callback to each of snd_pcm_ops table in ca0106
> that calls dma_mmap_coherent() above, or change snd_pcm_default_mmap
> to call dma_mmap_coherent() directly instead of nopage method.
> For the former way, take a look at sound/arm/aaci.c (and devdma.c) as
> a reference.
> 

I implemented the "former way".  However, when I put a breakpoint in
__dma_alloc_coherent it does not get called when I run speaker-test.
 It does get called during execution of "modprobe snd-ca0106".

Also, when I try to look at the memory allocated by the problematic
call to mmap in gdb, I get the following results:

Breakpoint 1, snd_pcm_mmap (pcm=0x10031880) at pcm_mmap.c:383
383                 ptr = mmap(NULL, size, PROT_READ|PROT_WRITE,
MAP_FILE|MAP_SHARED, i->u.mmap.fd, i->u.mmap.offset);
(gdb) n
384                 if (ptr == MAP_FAILED) {
(gdb) print (void *)ptr
$1 = (void *) 0x3001e000
(gdb) print ptr[0]
Cannot access memory at address 0x3001e000

So, while these changes eliminate the bugcheck, it does not appear
to be the correct solution.

-- 
Thank you,
David Cullen
Teligy
(864) 527-1263 Office
(864) 415-7063 Cell

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