Re: [PATCH v2 17/17] ASoC: fsl: add imx-sgtl5000 machine driver

[Sascha Hauer <s.hauer@pengutronix.de>]

On Mon, Mar 05, 2012 at 12:09:13PM -0600, Matt Sealey wrote:
> There is in the BSP but the BSP driver is trying to be way too fancy
> with I2S settings on the imx-ssi driver you wrote (it works well for
> AC97, but for SSI in I2S slave mode there are so many hacks upon hacks
> "they" have presented, it'd never mainline)
> 
> Having the codec provide clocks in slave mode works great in fsl-ssi
> because it doesn't set the chip up any other way, but I've had serious
> problems here whereby playing back a 48khz, 16-bit audio stream and
> recording in ANYTHING else seems to make the playback stream slow
> motion, but I can't trace whether it's the SSI config (seems unlikely
> as the only valid STXCCR bit in slave mode is the word length) or the
> codec config. In theory the playback and capture should be serialized
> by the driver, though, right? It wouldn't be possible to be a slave to
> the codec if it had to run the clock two different rates at the same
> time.. app1 sends a sample buffer, codec does dma, app2 requests
> capture buffer, codec does dma, they can't happen at the same time,
> maybe we are missing an important mutex or spinlock here that would
> enforce this and stop the configuration changing mid-stream.. I'm far
> from the ALSA expert though)
> 
> If adding capture support means having to make the SSI driver work in
> I2S master mode and do the laborious work of actually dividing the SSI
> clock, configuring the external PLL etc. so it can clock the codec
> appropriately for this mode then that's what will have to be done, and
> I agree with Sascha, whatever the solution it should be something that
> gets done now (not least because I kind of want audio here.. :) along
> with quite possibly adapting the current imx-ssi driver (as opposed to
> the fsl-ssi driver) to be fsl-ssi-ac97 vs fsl-ssi-imx so we have
> dedicated operation (which will make the AC97/FIQ select much easier
> to determine).

master mode shouldn't be necessary to get the sgtl5000 work with both
recording and playback. I have seen it working on the babbage board in
slave mode on some internal branch. I never got the sgtl5000 mainline
driver to work though.

> 
> While we're at it; did anyone patch arch/arm/mach-imx/ssi-fiq.S to be
> compiled in .arm mode yet? I can't find it in a tree or the list but I
> could be wrong. I am sure we mutually agreed (or at least Russell
> decided) on this to get thumb kernels to build again since none of the
> dependent processors/config selections are M-profile?

I think we agreed on compiliing this in arm mode but nobody has sent a
patch yet.

Sascha

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