Re: [PATCH MC Next Gen v2 2/3] sound/usb: Create media mixer function and control interface entities

[Takashi Iwai <tiwai@suse.de>]

On Tue, 03 Nov 2015 17:06:45 +0100,
Shuah Khan wrote:
> 
> On 10/25/2015 03:37 PM, Shuah Khan wrote:
> > On 10/22/2015 01:16 AM, Takashi Iwai wrote:
> >> On Wed, 21 Oct 2015 01:25:15 +0200,
> >> Shuah Khan wrote:
> >>>
> >>> Add support for creating MEDIA_ENT_F_AUDIO_MIXER entity for
> >>> each mixer and a MEDIA_INTF_T_ALSA_CONTROL control interface
> >>> entity that links to mixer entities. MEDIA_INTF_T_ALSA_CONTROL
> >>> entity corresponds to the control device for the card.
> >>>
> >>> Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
> >>> ---
> >>>   sound/usb/card.c     |  5 +++
> >>>   sound/usb/media.c    | 89
> >>> ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>>   sound/usb/media.h    | 20 ++++++++++++
> >>>   sound/usb/mixer.h    |  1 +
> >>>   sound/usb/usbaudio.h |  1 +
> >>>   5 files changed, 116 insertions(+)
> >>>
> >>> diff --git a/sound/usb/card.c b/sound/usb/card.c
> >>> index 469d2bf..d004cb4 100644
> >>> --- a/sound/usb/card.c
> >>> +++ b/sound/usb/card.c
> >>> @@ -560,6 +560,9 @@ static int usb_audio_probe(struct usb_interface
> >>> *intf,
> >>>       if (err < 0)
> >>>           goto __error;
> >>>
> >>> +    /* Create media entities for mixer and control dev */
> >>> +    media_mixer_init(chip);
> >>> +
> >>>       usb_chip[chip->index] = chip;
> >>>       chip->num_interfaces++;
> >>>       chip->probing = 0;
> >>> @@ -616,6 +619,8 @@ static void usb_audio_disconnect(struct
> >>> usb_interface *intf)
> >>>           list_for_each(p, &chip->midi_list) {
> >>>               snd_usbmidi_disconnect(p);
> >>>           }
> >>> +        /* delete mixer media resources */
> >>> +        media_mixer_delete(chip);
> >>>           /* release mixer resources */
> >>>           list_for_each_entry(mixer, &chip->mixer_list, list) {
> >>>               snd_usb_mixer_disconnect(mixer);
> >>> diff --git a/sound/usb/media.c b/sound/usb/media.c
> >>> index 0cbfee6..a26ea8b 100644
> >>> --- a/sound/usb/media.c
> >>> +++ b/sound/usb/media.c
> >>> @@ -199,4 +199,93 @@ void media_stop_pipeline(struct
> >>> snd_usb_substream *subs)
> >>>       if (mctl)
> >>>           media_disable_source(mctl);
> >>>   }
> >>> +
> >>> +int media_mixer_init(struct snd_usb_audio *chip)
> >>> +{
> >>> +    struct device *ctl_dev = &chip->card->ctl_dev;
> >>> +    struct media_intf_devnode *ctl_intf;
> >>> +    struct usb_mixer_interface *mixer;
> >>> +    struct media_device *mdev;
> >>> +    struct media_mixer_ctl *mctl;
> >>> +    u32 intf_type = MEDIA_INTF_T_ALSA_CONTROL;
> >>> +    int ret;
> >>> +
> >>> +    mdev = media_device_find_devres(&chip->dev->dev);
> >>> +    if (!mdev)
> >>> +        return -ENODEV;
> >>> +
> >>> +    ctl_intf = (struct media_intf_devnode *)
> >>> chip->ctl_intf_media_devnode;
> >>
> >> Why do we need cast?  Can't chip->ctl_intf_media_devnode itself be
> >> struct media_intf_devndoe pointer?
> > 
> > Yeah. There is no need to cast here. I will fix it.
> 
> Sorry I misspoke. The reason for this cast is ctl_intf_media_devnode
> is void to avoid including media.h and other media files in usbaudio.h

You can declare the struct without definition in each header file.
So just declare it and use it in usbaudio.h like:

struct media_intf_devnode;

struct snd_usb_audio {
	....
	struct media_intf_devnode *ctl_intf_media_devnode;
	....

And even if you're using a void pointer there instead of the explicit
struct pointer, the cast is superfluous.  The implicit cast between a
void pointer and any other pointer is valid in plain C.


Takashi