linux-kernel - Re: [PATCH 16/16] alsa sound support for mips

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Date:	Wed, 18 Apr 2007 22:13:02 +0800
From:	Fuxin Zhang <fxzhang@....ac.cn>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	tiansm@...ote.com, perex@...e.cz, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
	Fuxin Zhang <zhangfx@...ote.com>
Subject: Re: [PATCH 16/16] alsa sound support for mips


>>  		vaddr = runtime->dma_area + offset;
>> +#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)
>>     
>
> Please use CONFIG_MIPS instead of __mips__ in #if / #ifdefs.
>
> The question if #ifdefing is the right approach to solve this problem is
> something else but I think no, ....
>   
I would agree that it is quite ugly, but changing virt_to_page for it 
does not seem right either.
>   
>> +		page = virt_to_page(CAC_ADDR(vaddr));
>> +#else
>>  		page = virt_to_page(vaddr);
>> +#endif
>>     
>
> So this is needed because the MIPS virt_to_page is returning a unsuitable
> value if vaddress is not a KSEG0 (64-bit: cached XKPHYS) address which is
> what GFP allocations and the slab will return.  So now we have to deciede
> if
>
>  a) the MIPS __pa() should be changed to handle uncached addresses.
>  b) the sound code here is simply broken.
>
> Some drivers seem to allocate runtime->dma_area from vmalloc, so this
> whole area in the sound code is looking like built on quicksand ...
>   
>> +#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)
>> +	/* all mmap using uncached mode */
>> +	area->vm_page_prot = pgprot_noncached(area->vm_page_prot);
>> +	area->vm_flags |= ( VM_RESERVED | VM_IO);
>>     
>
> VM_RESERVED will prevent the buffer from being freed.  I assume that is
> another workaround for some kernel subsystem blowing up when being fed a
> pointer to an uncached RAM address?  This smells like a memory leak.
>
>   
Oh, VM_RESERVED should be a memory leak problem, we can remove it.
I don't remember any case of other subsystem's problem, just did not 
think much
to add those flags.
>> +#endif
>> +
>>  	offset = area->vm_pgoff << PAGE_SHIFT;
>>  	switch (offset) {
>>  	case SNDRV_PCM_MMAP_OFFSET_STATUS:
>> diff --git a/sound/core/sgbuf.c b/sound/core/sgbuf.c
>> index cefd228..535f0bc 100644
>> --- a/sound/core/sgbuf.c
>> +++ b/sound/core/sgbuf.c
>> @@ -91,12 +91,21 @@ void *snd_malloc_sgbuf_pages(struct device *device,
>>  		}
>>  		sgbuf->table[i].buf = tmpb.area;
>>  		sgbuf->table[i].addr = tmpb.addr;
>> +#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)
>> +		sgbuf->page_table[i] = virt_to_page(CAC_ADDR(tmpb.area));
>>     
>
> VM_RESERVED will prevent the buffer from being freed.  I assume that is
> another workaround for some kernel subsystem blowing up when being fed a
> pointer to an uncached RAM address?  This smells like a memory leak.
>
>   
>> +#else
>>  		sgbuf->page_table[i] = virt_to_page(tmpb.area);
>> +#endif
>>  		sgbuf->pages++;
>>  	}
>>  
>>  	sgbuf->size = size;
>> +#if defined(__mips__) && defined(CONFIG_DMA_NONCOHERENT)
>> +	/* maybe we should use uncached accelerated mode */
>> +	dmab->area = vmap(sgbuf->page_table, sgbuf->pages, VM_MAP | VM_IO, pgprot_noncached(PAGE_KERNEL));
>> +#else
>>  	dmab->area = vmap(sgbuf->page_table, sgbuf->pages, VM_MAP, PAGE_KERNEL);
>> +#endif
>>     
>
> I would suggest to get rid of this ifdef with a new arch-specific function
> like vmap_io_buffer which will do whatever a platform seems fit for this
> case?
>   
I think arch-specific function is the correct way, but don't know what 
the alsa gods think.
>   
>>  	if (! dmab->area)
>>  		goto _failed;
>>  	return dmab->area;
>>     
>
>   Ralf
>
>
>
>
>   
-
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