IIRC, a similar buffer handling (via vmalloc) is used in video drivers. I suppose they don't work as well, right?
Well, our FB driver is aware of the problem. I can't say much about other ones...
DRM driver uses __vmalloc() with PAGE_KERNEL_NOCACHE, but it's only for PPC32 non-coherent.
Hm. PPC with non-coherent cache?
/* * Only on coherent architectures, we can mmap the status and the control records * for effcient data transfer. On others, we have to use HWSYNC ioctl... */ #if defined(CONFIG_X86) || defined(CONFIG_PPC) || defined(CONFIG_ALPHA) ^^^^^^^^^^ /* * mmap status record */ static struct page * snd_pcm_mmap_status_nopage(struct vm_area_struct *area, unsigned long address, int *type)
x86 does it also, via its PAGE_AGP definition.
There are not that many platforms that define PAGE_KERNEL_NOCACHE though, so this gets a bit messy..
Oh, bloody hell, I haven't realised that!
Yeah, that's not sexy, but maybe the only working case right now
(better with arch-specific ifdefs).
The question is what ifdefs to use ;-) Because the cached/uncached decision must be consistent between snd_pcm_default_mmap() and buffer allocation...
What a mess! ;-)
Paweł