Re: new ALSA driver for audio on the ARM PXA2xx platform

[Takashi Iwai <tiwai@suse.de>]

Hi Nicolas,

At Tue, 25 Jan 2005 16:33:40 -0500 (EST),
Nicolas Pitre wrote:
> 
> 
> This patch adds two modules: one for generic PCM support on PXA2xx and 
> another to interface with the AC97 link on the PXA2xx.  Eventually 
> additional modules could be written to use the PCM module with SSP or 
> I2S audio ports.
> 
> Signed-off-by: Nicolas Pitre <nico@cam.org>

Thanks, the code looks nice.


> +static int pxa2xx_ac97_pcm_startup(snd_pcm_substream_t *substream)
> +{
> +	snd_pcm_runtime_t *runtime = substream->runtime;
> +	pxa2xx_audio_ops_t *platform_ops;
> +	int vra_mask;
> +
> +	runtime->hw.channels_min = 2;
> +	runtime->hw.channels_max = 2;
> +
> +	vra_mask = (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) ?
> +		   AC97_EA_VRA : AC97_EA_VRM;
> +	if (pxa2xx_ac97_ac97->regs[AC97_EXTENDED_STATUS] & vra_mask) {
> +		runtime->hw.rates = SNDRV_PCM_RATE_8000_48000;
> +		runtime->hw.rate_min = 8000;
> +		runtime->hw.rate_max = 48000;
> +	} else {
> +		runtime->hw.rates = SNDRV_PCM_RATE_48000;
> +		runtime->hw.rate_min = 48000;
> +		runtime->hw.rate_max = 48000;
> +	}

You can use ac97->rates[AC97_RATES_FRONT_DAC] and
ac97->rates[AC97_RATES_ADC] for rates bits, and call
snd_pcm_limit_hw_rates(runtime) to set rate_min/max automatically.

Some codecs don't support non-standard rate even VRA is set.


> +static int pxa2xx_ac97_probe(struct device *dev)
(snip)
> +	snprintf(card->shortname, sizeof(card->shortname), "%s",
> +		 snd_ac97_get_short_name(pxa2xx_ac97_ac97));

Set longname, too.  It will appear in /proc/asound/cards.

> Index: linux-2.6/sound/arm/pxa2xx-pcm.c
(snip)
> +static const snd_pcm_hardware_t pxa2xx_pcm_hardware = {
> +	.info			= SNDRV_PCM_INFO_MMAP |
> +				  SNDRV_PCM_INFO_MMAP_VALID |
> +				  SNDRV_PCM_INFO_INTERLEAVED |
> +				  SNDRV_PCM_INFO_PAUSE,

Don't forget SNDRV_PCM_INFO_RESUME if the driver supports PM.

> +	.formats		= SNDRV_PCM_FMTBIT_S16_LE,
> +	.period_bytes_min	= 32,
> +	.period_bytes_max	= 8192 - 32,

I suppose this 32 is fifo size?  If so, you don't have to count it
here.  The period size defines the size of DMA interrupt period.
(The fifo_size isn't used in the driver currently.)

> +static void pxa2xx_pcm_dma_irq(int dma_ch, void *dev_id, struct pt_regs *regs)
> +{
> +	snd_pcm_substream_t *substream = dev_id;
> +	struct pxa2xx_runtime_data *rtd = substream->runtime->private_data;
> +	int dcsr;
> +
> +	dcsr = DCSR(dma_ch);
> +	DCSR(dma_ch) = dcsr & ~DCSR_STOPIRQEN;
> +
> +	if (dcsr & DCSR_ENDINTR) {
> +		snd_pcm_period_elapsed(substream);
> +	} else {
> +		printk( KERN_ERR "%s: DMA error on channel %d (DCSR=%#x)\n",
> +			rtd->params->name, dma_ch, dcsr );

You can call here snd_pcm_stop(substream, SNDRV_PCM_STATE_XRUN) to
notify the buffer over/underrun.


> +static int
> +pxa2xx_pcm_mmap(snd_pcm_substream_t *substream, struct vm_area_struct *vma)
> +{
> +	snd_pcm_runtime_t *runtime = substream->runtime;
> +	return dma_mmap_writecombine(substream->pcm->card->dev, vma,
> +				     runtime->dma_area,
> +				     runtime->dma_addr,
> +				     runtime->dma_bytes);
> +}
> +
> +static snd_pcm_ops_t pxa2xx_pcm_ops = {
> +	.open		= pxa2xx_pcm_open,
> +	.close		= pxa2xx_pcm_close,
> +	.ioctl		= snd_pcm_lib_ioctl,
> +	.hw_params	= pxa2xx_pcm_hw_params,
> +	.hw_free	= pxa2xx_pcm_hw_free,
> +	.prepare	= pxa2xx_pcm_prepare,
> +	.trigger	= pxa2xx_pcm_trigger,
> +	.pointer	= pxa2xx_pcm_pointer,
> +	.mmap		= pxa2xx_pcm_mmap,
> +};

Heh, finally a right driver using mmap callback ;)


Takashi


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