Re: [RFC 01/xx] ALSA: add snd_stream_is_playback/capture() macro

[Kuninori Morimoto <kuninori.morimoto.gx@xxxxxxxxxxx>]

Hi Amadeusz, Takashi

> > Perhaps you could use generics here, so you could have one caller for
> > both cases?
> > 
> > Something like:
> > #define snd_pcm_is_playback(x) _Generic((x),                   \
> >         int :         (x == SNDRV_PCM_STREAM_PLAYBACK), \
> >         struct snd_pcm_substream *substream * : (x->stream ==
> > SNDRV_PCM_STREAM_PLAYBACK))(x)
> > or just call the above functions in it?

Hmm... I couldn't compile above inline style.
I need to create function, and use it on _Generic().

And then, _Generic() is very picky for variable sytle.
This means I need to create function for "int" / "const int",
"unsigned int", "const unsigned int"

static inline int snd_pcm_stream_is_playback_(const int stream)
{
	return stream == SNDRV_PCM_STREAM_PLAYBACK;
}

static inline int snd_pcm_stream_is_playback(int stream)
{
	return stream == SNDRV_PCM_STREAM_PLAYBACK;
}

static inline int snd_pcm_stream_is_playback_u(const unsigned int stream)
{
	return stream == SNDRV_PCM_STREAM_PLAYBACK;
}

static inline int snd_pcm_stream_is_playbacku(unsigned int stream)
{
	return stream == SNDRV_PCM_STREAM_PLAYBACK;
}

static inline int snd_pcm_substream_is_playback_(const struct snd_pcm_substream *substream)
{
	return snd_pcm_stream_is_playback(substream->stream);
}

static inline int snd_pcm_substream_is_playback(struct snd_pcm_substream *substream)
{
	return snd_pcm_stream_is_playback(substream->stream);
}

#define snd_pcm_is_playback(x) _Generic((x), \
	const int : snd_pcm_stream_is_playback_, \
	      int : snd_pcm_stream_is_playback, \
	const unsigned int : snd_pcm_stream_is_playback_u, \
	      unsigned int : snd_pcm_stream_is_playbacku, \
	const struct snd_pcm_substream * : snd_pcm_substream_is_playback_, \
	      struct snd_pcm_substream * : snd_pcm_substream_is_playback)(x)

And I'm not sure how to handle "bit field" by _Generic.

	${LINUX}/sound/pci/ac97/ac97_pcm.c:153:13: note: in expansion of macro 'snd_pcm_is_playback'
	  153 |         if (snd_pcm_is_playback(pcm->stream))
	      |             ^~~~~~~~~~~~~~~~~~~
	${LINUX}/sound/pci/ac97/ac97_pcm.c: In function 'snd_ac97_pcm_assign':
	${LINUX}/include/sound/pcm.h:544:41: error: '_Generic' selector of type 'unsigned char:1' is not compatible with any association
	  544 | #define snd_pcm_is_playback(x) _Generic((x), \

Not using _Generic() is easy, "const int" version can handle everything
(= "int", "const int", "unsigned int", "const unsigned int", "short",
"const short", "bit field", etc).

If there is better _Generic() grammar, I can follow it.
If there wasn't, unfortunately let's give up this conversion...

Thank you for your help !!

Best regards
---
Kuninori Morimoto