Re: DMA feature question.

[James Courtier-Dutton <James@superbug.demon.co.uk>]

Takashi Iwai wrote:
>>If not, I will just have to make (1) a bit bigger, and place the "table 
>>of periods" in there.
> 
> 
> I don't think it's a good idea.
> The buffer will be mmapped to the user-space, and obviously you don't
> want to expose it.

The terms "Massive security hole!" comes to mind!

> 
> I'd suggest to allocate a table (one page should be large enough) via
> snd_dma_alloc_pages() statically at the driver initialization, and
> sets the max. number of periods according to the page size.
> 
> 
> Takashi
> 
> 

Is a page 1024 bytes or 4096 bytes? Does it vary depending on which type 
of CPU is in use? Is there a sensible minimum size to set it.

I only need to allow for a max of 16 periods per buffer. (does anyone 
need >16 periods per buffer ? )
There are 4 channels, with 8 bytes per period, that gives 16*4*8 = 512 
bytes.

Thanks, I will use snd_dma_alloc_pages().
For your info, this is for the AudigyLS driver.

Cheers
James


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