On Wed, 24 Feb 2021 09:14:41 +0100, Jaroslav Kysela wrote: > > Dne 24. 02. 21 v 8:12 Takashi Iwai napsal(a): > > On Tue, 23 Feb 2021 21:56:16 +0100, > > Jaroslav Kysela wrote: > >> > >> Dne 23. 02. 21 v 17:20 Takashi Iwai napsal(a): > >>>>> Of course, this implementation would make the integration much easier, > >>>>> and that's a big benefit. So I have a mixed feeling and not decided > >>>>> yet whether we should go for it right now... > >>>> > >>>> I think that we can reconsider the LED handling implementation later, when > >>>> someone brings something better on the table. > >>> > >>> What worried me is the plan to expose this capability to user-space. > >>> If it's only a kernel-internal, we can fix it in the kernel and > >>> nothing else broken, but if it's a part of API, that's not easy. > >>> > >>> So, if any, I'd like to avoid exposing to the user-space at first. > >>> (But then it comes to the question how to deal with a case like AMD > >>> ACP...) > >> > >> I tried to propose a complete solution and the ACP was one strong reason for > >> this kernel / user space API. So without the user space support, it's just > >> a half solution for known issues. > >> > >> Frankly, I don't see any drawback or a problem even if we remove this API > >> later. > > > > Removing the user-space API is absolutely no-go. The only exception > > would be either the case really no one uses it or it's too buggy and > > unfixable. > > This is a special case. Even if those LED bits are ignored by kernel in > future, we expect to be replaced with another layer. Thus the functionality > must be retained. Well, we cannot know whether the replacement really happens or happened, and hence we never kill the old one. That's the problem. > >> The LED group bits are just informal for the user space and it's > >> expected to create the user controls tied to this LED functionality only in > >> alsa-lib/plugins at the moment. The kernel may return an error when the user > >> space tries to set those new bits when the API is deprecated and I believe > >> that the hardware design faults like AMD ACP (without the hardware mute) are rare. > > > > The experience tells us that users are creative enough to (ab)use a > > new ABI in any unexpected ways, and we have no control for it. So > > it's not about how alsa-lib is implemented but rather how ABI could be > > abused :) > > Ok, I don't have other ideas. I don't agree with your argumentation for this > particular case, where the functionality is marginal. Ideally, the AMD driver > may be recoded to use double-buffering and software mute switch, so we should > handle everything in the kernel space. My argument is that we're trying to add too much freedom just for this "marginal" problem. Honestly speaking, I would feel rather more comfortable if it were a kernel control element that just does trigger the LED like the original patch from AMD guys. Then you cannot do much wrong. OTOH, creating a virtual capture switch and let alsa-lib handling the software mute, while PA should ignores the soft-mute but dealing only with the assigned mute LED... Sounds too complex to me. thanks, Takashi
