sound/core/oss/linear.c

Source file repositories/reference/linux-study-clean/sound/core/oss/linear.c

File Facts

System
Linux kernel
Corpus path
sound/core/oss/linear.c
Extension
.c
Size
5135 bytes
Lines
166
Domain
Driver Families
Bucket
sound/core
Inferred role
Driver Families: implementation source
Status
source implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

struct linear_priv {
	int cvt_endian;		/* need endian conversion? */
	unsigned int src_ofs;	/* byte offset in source format */
	unsigned int dst_ofs;	/* byte soffset in destination format */
	unsigned int copy_ofs;	/* byte offset in temporary u32 data */
	unsigned int dst_bytes;		/* byte size of destination format */
	unsigned int copy_bytes;	/* bytes to copy per conversion */
	unsigned int flip; /* MSB flip for signeness, done after endian conv */
};

static inline void do_convert(struct linear_priv *data,
			      unsigned char *dst, unsigned char *src)
{
	unsigned int tmp = 0;
	unsigned char *p = (unsigned char *)&tmp;

	memcpy(p + data->copy_ofs, src + data->src_ofs, data->copy_bytes);
	if (data->cvt_endian)
		tmp = swab32(tmp);
	tmp ^= data->flip;
	memcpy(dst, p + data->dst_ofs, data->dst_bytes);
}

static void convert(struct snd_pcm_plugin *plugin,
		    const struct snd_pcm_plugin_channel *src_channels,
		    struct snd_pcm_plugin_channel *dst_channels,
		    snd_pcm_uframes_t frames)
{
	struct linear_priv *data = (struct linear_priv *)plugin->extra_data;
	int channel;
	int nchannels = plugin->src_format.channels;
	for (channel = 0; channel < nchannels; ++channel) {
		char *src;
		char *dst;
		int src_step, dst_step;
		snd_pcm_uframes_t frames1;
		if (!src_channels[channel].enabled) {
			if (dst_channels[channel].wanted)
				snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
			dst_channels[channel].enabled = 0;
			continue;
		}
		dst_channels[channel].enabled = 1;
		src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
		dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
		src_step = src_channels[channel].area.step / 8;
		dst_step = dst_channels[channel].area.step / 8;
		frames1 = frames;
		while (frames1-- > 0) {
			do_convert(data, dst, src);
			src += src_step;
			dst += dst_step;
		}
	}
}

static snd_pcm_sframes_t linear_transfer(struct snd_pcm_plugin *plugin,
			       const struct snd_pcm_plugin_channel *src_channels,
			       struct snd_pcm_plugin_channel *dst_channels,
			       snd_pcm_uframes_t frames)
{
	if (snd_BUG_ON(!plugin || !src_channels || !dst_channels))
		return -ENXIO;
	if (frames == 0)
		return 0;
#ifdef CONFIG_SND_DEBUG
	{
		unsigned int channel;
		for (channel = 0; channel < plugin->src_format.channels; channel++) {
			if (snd_BUG_ON(src_channels[channel].area.first % 8 ||
				       src_channels[channel].area.step % 8))
				return -ENXIO;
			if (snd_BUG_ON(dst_channels[channel].area.first % 8 ||
				       dst_channels[channel].area.step % 8))
				return -ENXIO;
		}
	}
#endif
	if (frames > dst_channels[0].frames)
		frames = dst_channels[0].frames;
	convert(plugin, src_channels, dst_channels, frames);
	return frames;
}

static void init_data(struct linear_priv *data,
		      snd_pcm_format_t src_format, snd_pcm_format_t dst_format)
{
	int src_le, dst_le, src_bytes, dst_bytes;

	src_bytes = snd_pcm_format_width(src_format) / 8;

Annotation

Implementation Notes