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Date: Sat, 27 Oct 2001 04:08:47 -0400
From: Jeff Garzik <jgarzik@mandrakesoft.com>
Organization: MandrakeSoft
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To: Pavel Roskin <proski@gnu.org>
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Subject: Re: [PATCH] More ioctls for VIA sound driver, Flash 5 now fixed
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Jeff Garzik wrote:
> So, the preferred allocation algorithm would be:
> 
>         if (OSS fragment size <= PAGE_SIZE)
>                 allocate chan->pgtbl[] in PAGE_SIZE chunks
>         else
>                 allocate chan->pgtbl[] in oss_frag_size chunks
> 
> Another key thing to rememeber is that pci_alloc_consistent usually
> returns a -minimum- of one page, so it's useless to allocate less than
> that, without switching the entire driver to the pci_pool_xxx API.

Another limitation, I just remembered:  Each scatter-gather buffer must
be a multiple of PAGE_SIZE (actually probably PAGE_CACHE_SIZE), in order
for mmap(2) support (via_mm_nopage) to work properly.

I would also like to point out that mmap support via
vm_operations_struct::nopage is also unique and new, and was suggested
by Linus as a much better mmap(2) approach than other drivers, which
using remap_page_range [a method which requires the one-big-buffer
allocation approach].

	Jeff


-- 
Jeff Garzik      | Only so many songs can be sung
Building 1024    | with two lips, two lungs, and one tongue.
MandrakeSoft     |         - nomeansno

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