[RFC PATCH 1/3] ALSA: control: add kcontrol_type to control

[Jaska Uimonen]

On Fri, Jan 08, 2021 at 11:06:59PM +0900, Takashi Sakamoto wrote:
> Hi,
> 
> On Fri, Jan 08, 2021 at 12:40:28PM +0100, Jaroslav Kysela wrote:
> > Dne 08. 01. 21 v 12:23 Jaska Uimonen napsal(a):
> > > Current kcontrol structs don't have a member to describe the control
> > > type. The type is present in the widget which contains the control. As
> > > there can be many controls in one widget it is inherently presumed that
> > > the control types are the same.
> > > 
> > > Lately there has been use cases where different types of controls would
> > > be needed for single widget. Thus enable this by adding the control type
> > > to kcontrol and kcontrol_new structs.
> > 
> > It looks like a SoC only extension. Use private_data to carry this
> > information. It has no value for the toplevel code.
> > 
> > 				Jaroslav
> 
> In current design of ALSA control core, the type of control element is
> firstly determined by driver in callback of snd_kcontrol.info(). The
> callback is done when userspace applications call ioctl(2) with
> SNDRV_CTL_IOCTL_ELEM_INFO request.
> 
> The patch doesn't touch to the above processing. It means that the type
> information is just for kernel-land implementation and is not exposed to
> userspace application.
> 
> Essentially, driver is dominant to determine the type of control element
> in control element set which the driver adds. It's possible to achieve
> your intension without changing ALSA control core itself, in my opinion.
> 
> As Jaroslav said, it's better to change core of ALSA SoC part according
> to your intention. If you'd like to change ALSA control core, I'd like
> to request for the check of mismatch between the value of added member
> in snd_kcontrol and the value of type of control element returned from
> driver, like:
> 
> ```
> diff --git a/sound/core/control.c b/sound/core/control.c
> index 809b0a62e..c3ae70574 100644
> --- a/sound/core/control.c
> +++ b/sound/core/control.c
> @@ -973,6 +973,7 @@ static int __snd_ctl_elem_info(struct snd_card *card,
>         result = kctl->info(kctl, info);
>         if (result >= 0) {
>                 snd_BUG_ON(info->access);
> +               snd_BUG_ON(info->type == kctl->kcontrol_type);
>                 index_offset = snd_ctl_get_ioff(kctl, &info->id);
>                 vd = &kctl->vd[index_offset];
>                 snd_ctl_build_ioff(&info->id, kctl, index_offset);
> ```
> 
> 
> Regards
> 
> Takashi Sakamoto

Hi,

Thanks for the comments, I tried to do the same thing now in asoc level, 
will send v2.

br,
Jaska