On Tue, Jul 09, 2013 at 11:36:26PM +0000, Linux Kernel wrote:
> Gitweb:
> http://git.kernel.org/linus/;a=commit;h=99a2008d0b32d72dfc2a54e7be1eb698dd2e3bd6
> Commit: 99a2008d0b32d72dfc2a54e7be1eb698dd2e3bd6
> Parent: 5c90680e42b08a1e4a6800ca02e75ad201f8037f
> Author: Wang Xingchao <[email protected]>
> AuthorDate: Thu May 30 22:07:10 2013 +0800
> Committer: Daniel Vetter <[email protected]>
> CommitDate: Thu Jun 6 17:31:56 2013 +0200
>
> ALSA: hda - Add power-welll support for haswell HDA
>
> For Intel Haswell chip, HDA controller and codec have
> power well dependency from GPU side. This patch added support
> to request/release power well in audio driver. Power save
> feature should be enabled to get runtime power saving.
>
> There's deadlock when request_module(i915) in azx_probe.
> It looks like:
> device_lock(audio pci device) -> azx_probe -> module_request
> (or symbol_request) -> modprobe (userspace) -> i915 init ->
> drm_pci_init -> pci_register_driver -> bus_add_driver -> driver_attach ->
> which in turn tries all locks on pci bus, and when it tries the one on
> the
> audio device, it will deadlock.
>
> This patch introduce a work to store remaining probe stuff, and let
> request_module run in safe work context.
That deadlock sounds nasty, but..
> +#ifdef CONFIG_SND_HDA_I915
> + probe_now = false;
> + schedule_work(&chip->probe_work);
> +#else
> + snd_printk(KERN_ERR SFX "Haswell must build in
> CONFIG_SND_HDA_I915\n");
> +#endif
runtime surprises like this are also a pain. There has to be a way in Kconfig
to express this (through addition of a new option). Though having to build this
in for distro kernels is also unfortunate. This means we'll also have to
build-in
all the ALSA stuff even for users who never use it.
Dave
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