Messages in this thread | | | Date | Fri, 28 Jul 2006 13:33:10 +0200 | From | Takashi Iwai <> | Subject | Re: Sound problems with snd_hda on x86_64 |
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At Fri, 28 Jul 2006 12:47:11 +0200, Denis Vlasenko wrote: > > On Friday 28 July 2006 12:29, Takashi Iwai wrote: > > > Which is, in turn, is caused by this code: > > > > > > --- linux-2.6.17.6.org/sound/core/pcm_compat.c 2006-07-15 21:00:43.000000000 +0200 > > > +++ linux-2.6.17.6.src/sound/core/pcm_compat.c 2006-07-28 00:35:10.000000000 +0200 > > > @@ -478,6 +478,8 @@ static long snd_pcm_ioctl_compat(struct > > > * mmap of PCM status/control records because of the size > > > * incompatibility. > > > */ > > > +printk("substream->no_mmap_ctrl = 1 in %s:%s line %d\n", __FILE__, __FUNCTION__, __LINE__); > > > +dump_stack(); > > > substream->no_mmap_ctrl = 1; > > > > > > switch (cmd) { > > > > > > It's puzzling. Even a 486 processor, can do 64-bit operations (using cmpxchg8) > > > on memory-mapped areas, why does code disallows mmap for 64-bit CPUs but allows > > > for 32-bit ones? > > > > On the contrary, the driver disallows mmap for 32bit task on 64bit > > architecture. This is because the size of the mapped record is > > different between 32bit and 64bit architectures, so it cannot be > > shared. > > Why artsd attempts mmap at all then?
The app must try mmap. From the application side, you can't know whether you're 32bit-emulation mode or it's really on 32bit architecture. And, mmap is usually done automatically via alsa-lib plugin for optimization or soft-mixing purpose.
> Why it thinks that > /dev/snd/pcmC0D0p is mmap-able when it is not?
Dunno. pcm_compat.c is only for 32bit context on 64bit architecture. The 64bit program will never go there.
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