2015-12-09 0:10 GMT+08:00 Takashi Iwai tiwai@suse.de:
Many codecs, typically found on Realtek codecs, have the analog loopback path merged to the secondary input of the middle of the output paths. Currently, we don't offer the dynamic switching in such configuration but let each loopback path mute by itself.
This should work well in theory, but in reality, we often see that such a dead loopback path causes some background noises even if all the elements get muted. Such a problem has been fixed by adding the quirk accordingly to disable aamix, and it's the right fix, per se. The only problem is that it's not so trivial to achieve it; user needs to pass a hint string via patch module option or sysfs.
This patch gives a bit improvement on the situation: it adds "Loopback Mixing" control element for such codecs like other codecs (e.g. IDT or VIA codecs) with the individual loopback paths. User can turn on/off the loopback path simply via a mixer app.
For keeping the compatibility, the loopback is still enabled on these codecs. But user can try to turn it off if experiencing a suspicious background or click noise on the fly, then build a static fixup later once after the problem is addressed.
Other than the addition of the loopback enable/disablement control, there should be no changes.
How about the amp in at those mixers of surround jacks / mio jacks ?