[alsa-devel] Hoping to enhance cs5535 driver - initial question

[Vince Negri]

Hi All,

I'm looking to enhance the cs5535 driver (Geode companion device) so
that it can support 5.1 operation when used with an appropriate AC97
codec. AFAIK, the existing ALSA driver only supports 2-channel
operation.

Having looked at the existing driver, and Takashi Iwai's guide, there
is still something I'm not too clear on - I hope you can set me
straight.

According to the AMD datasheet, when used in 5.1 mode the cs5535 makes
use of 4 distinct DMAs - the first (BM0) is the main L/R pair, and
this is the one used by the existing driver. There is another DMA for
L/R surround, another for the centre channel, and the fourth DMA feeds
the LFE channel. Two stereos and two monos.

I'm comfortable with the low-level bit bashing: what I'm unsure of is
what is necessary to represent all of this to the upper layers so that
the ALSA clients see me as a 6-channel device.
Do I need to represent the 4 DMAs as substreams of the playback pcm,
for example? Or have I completely misunderstood what a substream is?

Alternatively, pointers to an existing driver that faces the same
issue would be very welcome.

Vince