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:
> At Mon, 27 Nov 2006 17:01:52 -0500,
> David Cullen wrote:
>> 
>> I am trying to get ALSA version 1.0.13 working on an AMCC PowerPC
>> PPC405EP Taihu board with a Sound Blaster Live! 24-bit 7.1 PCI card.
>>  I am using a patched 2.6.13 kernel that comes with the board.  I
>> built the kernel with the sound core built in and I used the
>> cross-compiler tools to build the ALSA driver, library, and utils.
>> When I run "speaker-test", it crashes in the ALSA library.  The
>> problem is that the call to mmap in
>> 
>>    alsa-lib-1.0.13/src/pcm/pcm_mmap.c line 367
>> 
>> which looks like
>> 
>>    ptr = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_FILE|MAP_SHARED,
>> i->u.mmap.fd, i->u.mmap.offset);
>> 
>> returns a pointer that appears to be valid (0x3001E000) but causes a
>> kernel OOPS when accessed.
>> 
>> Previous calls to mmap in pcm_hw.c on lines 822 and 854 both
>> succeed, and the pointers returned can be successfully accessed, but
>> they use the status and control offsets as parameters to mmap.
>> 
>> I haved traced the problem on the target into the ALSA library using
>> gdb and into the kernel using kgdb and everything looks like it
>> works properly.  If I disable the semaphore acquisition in do_mmap2,
>> I can print the contents of the address in kgdb using
>> 
>>    (gdb) print ((char *)vma->vm_start)[0]
>> 
>> after the call to vm_link in do_mmap_pgoff.  However, the board
>> locks up after the print command.
>> 
>> Anyone have any experience with this type of problem on PowerPC systems?
> 
> Possibly a memory coherency problem.  The memory allocated via
> dma_alloc_coherent() isn't simply mmappable.
> 
> An essential fix would be to add dma_mmap_coherent() to all
> architectures and use it for ALSA mmap.  I made some patches quite
> ago, but left it rotten for the time being...
> 

The kernel I am using has this line in the .config file

   CONFIG_NOT_COHERENT_CACHE=y

It also has

   arch\ppc\kernel\dma-mapping.c

with

/*
 * Allocate DMA-coherent memory space and return both the kernel
remapped
 * virtual and bus address for that space.
 */
void *
__dma_alloc_coherent(size_t size, dma_addr_t *handle, int gfp)

defined and

   include\asm-ppc\dma-mapping.h

with

static inline void *dma_alloc_coherent(struct device *dev, size_t size,
                       dma_addr_t * dma_handle, int gfp)
{
#ifdef CONFIG_NOT_COHERENT_CACHE
    return __dma_alloc_coherent(size, dma_handle, gfp);
#else

defined.  However, if I put a breakpoint in __dma_alloc_coherent, it
does not appear to get called.  Is there something special I have to
do to ALSA to get it to use the ppc version of dma_alloc_coherent?

Pardon me for e-mailing you directly if that was not polite behavior
for this list.

-- 
Thank you,
David Cullen
Teligy

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