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From: Takashi I. <ti...@su...> - 2007-02-26 15:31:54
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At Sat, 24 Feb 2007 23:20:17 -0200, Henrique de Moraes Holschuh wrote: > > Hello, > > I am the current maintainer of the ibm-acpi driver for the Linux kernel. > Those of you that own a ThinkPad notebook probably know what I am talking > about. > > A ThinkPad notebook has a hardware mixer for volume control (two functions: > volume and mute). The user can interact with this volume control using > three buttons (up/down/mute), and it is completely implemented in firmware. > > ibm-acpi currently exports those controls through a procfs interface, but I > am trying to get rid of it, and instead of just porting the interface to > sysfs attributes, I tried to write a proof-of-concept alsa mixer -- if it is > a mixer, it should be exported as one, not as some driver-specific sysfs > attributes, IMHO :-) > > It worked almost perfectly, and it was easy to write. Many thanks to > Takashi Iwai for his excellent docs at > http://www.alsa-project.org/~iwai/writing-an-alsa-driver/index.html. > > The only issue was in userspace, apparently alsamixer ignores VOLATILE > controls and doesn't poll them for updates. I wonder how widespread such > misbehaviour is? I may have to write an in-driver polling thread so that I > can send notifications, if it is too widespread. That's exactly the role of VOLATILE flag. It's for controls with frequently changing elements (e.g. VU-meters) and thus not suitable for poll/select by a mixer app. I think the case of volume buttons is OK to use normal controls without VOLATILE flag. > Anyway, the driver is *not* a stand-alone module, but rather just a small > part of ibm-acpi. I suppose I could break it into two modules so that the > alsa mixer has its own module, but either it would *have* to depend on > ibm-acpi, or it would have to duplicate a lot of thinkpad specific stuff. > > How do you guys feel about an in-tree module that has alsa stuff in it, but > is not part of the alsa tree? Would that be a problem? I'm basically for including it in ALSA driver (suppose intel8x0?) as long as it's directly related with the sound. If you have a working patch, I'm willing to review and discuss more. Anyway, the reply will be delayed since I'll be in vacation from now for a week or so. Thanks, Takashi |
