Hi Takashi,
On 2/6/2024 4:57 AM, Takashi Iwai wrote:
On Sat, 03 Feb 2024 03:36:40 +0100, Wesley Cheng wrote:
In order to allow userspace/applications know about USB offloading status, expose a sound kcontrol that fetches information about which sound card index is associated with the ASoC platform card supporting offloading. In the USB audio offloading framework, the ASoC BE DAI link is the entity responsible for registering to the SOC USB layer. SOC USB will expose more details about the current offloading status, which includes the USB sound card and USB PCM device indexes currently being used.
Signed-off-by: Wesley Cheng quic_wcheng@quicinc.com
The concept is understandable, but the control element name ("SNDUSB OFFLD playback available") looks non-intrusive and non-conformant. Use a bit more understandable name instead.
This provides a card number where the offload driver is bound, and the name should indicate something about that.
Hmmm, does USB sound have a naming convention that it usually follows for mixer/control interfaces?
For something that is more closely related, how about: "USB offload capable card"
Also, about the implementation:
+static int +snd_usb_offload_create_mixer(struct usb_mixer_interface *mixer,
const struct snd_kcontrol_new *new_kctl)+{
- struct snd_kcontrol *kctl;
- struct usb_mixer_elem_info *elem;
- elem = kzalloc(sizeof(struct usb_mixer_elem_info), GFP_KERNEL);
- if (!elem)
return -ENOMEM;- elem->head.mixer = mixer;
- elem->val_type = USB_MIXER_S32;
- elem->control = 0;
- elem->head.id = 0;
- elem->channels = 1;
- kctl = snd_ctl_new1(new_kctl, elem);
- if (!kctl) {
kfree(elem);return -ENOMEM;- }
- kctl->private_free = snd_usb_mixer_elem_free;
- return snd_usb_mixer_add_control(&elem->head, kctl);
This control has almost little to do with the standard USB interface, and it'll be much simpler if you create a raw control element. Pass the bus or the sysdev to private_data, and that's all you need in the get callback.
Sure, I'll remove the need to register over the SND USB mixer API, and just use the core SND control APIs.
Also, don't forget to set the proper access bits (it's read-only).
Thanks for pointing this out, will fix.
Thanks Wesley Cheng
thanks,
Takashi