[alsa-devel] [PATCH 07/11] ASoC: tegra: Add tegra-das driver

[Stephen Warren]

Mark Brown wrote:
> On Fri, Dec 17, 2010 at 02:41:26PM -0700, Stephen Warren wrote:
> 
> > /*
> >  * Terminology:
> >  * DAS: Digital audio switch (HW module controlled by this driver)
> >  * DAP: Digital audio port (port/pins on Tegra device)
> >  * DAC: Digital audio controller (e.g. I2S or AC97 controller elsewhere)
> >  * 
> >  * The Tegra DAS is a mux/cross-bar which can connect each DAP to a specific
> >  * DAC, or another DAP. When DAPs are connected, one must be the master and
> >  * one the slave. Each DAC allows selection of a specific DAP for input, to
> >  * cater for the case where N DAPs are connected to 1 DAC for broadcast
> >  * output.
> >  *
> >  * This driver is dumb; no attempt is made to ensure that a valid routing
> >  * configuration is programmed.
> >  */ 
> 
> Reading this it's essentially just exporting point to point switches
> within the DAS block.  This really feels like it ought to be represented
> as a CODEC driver to give runtime flexibility to userspace to control
> the mux - it looks like the AP part of the system streams data into this
> block which then has very flexible switching on to the externally
> connected audio devices.

Hmm. I don't see any examples of anything like Tegra's DAS in the existing
ASoC code-base. So, I'm slightly unsure how to recast the DAS driver as
a codec. In particular, in the machine driver, would I do something like:

static struct snd_soc_dai_link harmony_i2s_das_link = {
	.name = "WM8903",
	.stream_name = "WM8903 PCM",
	.cpu_dai_name = "tegra-i2s-dai.0",
	.platform_name = "tegra-pcm-audio",
	.codec_name = "tegra-das.0",
	.codec_dai_name = "tegra-das.0-in",
	.ops = &harmony_i2s_das_ops,
};

static struct snd_soc_dai_link harmony_das_wm8903_link = {
	.cpu_dai_name = "tegra-das.0-out",
	.codec_name = "wm8903-codec.0-001a",
	.codec_dai_name = "wm8903-hifi",
	.ops = &harmony_das_codec_ops,
};

static struct snd_soc_dai_link *harmony_links[] = {
	& harmony_i2s_das_link,
	& harmony_das_wm8903_link,
};

static struct snd_soc_card snd_soc_harmony = {
	.name = "tegra-harmony",
	.dai_link = &harmony_links,
	.num_links = ARRAY_SIZE(harmony_links),
};

And then re-write the tegra-das driver to expose two DAIs somehow?

Wouldn't that end up exposing two streams to user-space, one for each entry
in harmony_links[]?

-- 
nvpublic