Re: [RFC PATCH 5/5] ASoC: omap-mcbsp: Place correct constraints for streams

[Peter Ujfalusi <peter.ujfalusi@nokia.com>]

On Monday 31 May 2010 11:16:50 Ujfalusi Peter (Nokia-D/Tampere) wrote:
...

> @@ -185,33 +231,43 @@ static int omap_mcbsp_dai_startup(struct
> snd_pcm_substream *substream, if (!cpu_dai->active)
>  		err = omap_mcbsp_request(bus_id);
> 
> +	/*
> +	 * OMAP McBSP FIFO is word structured.
> +	 * McBSP2 has 1024 + 256 = 1280 word long buffer,
> +	 * McBSP1,3,4,5 has 128 word long buffer
> +	 * This means that the size of the FIFO depends on the sample format.
> +	 * For example on McBSP3:
> +	 * 16bit samples: size is 128 * 2 = 256 bytes
> +	 * 32bit samples: size is 128 * 4 = 512 bytes
> +	 * It is simpler to place constraint for buffer and period based on
> +	 * channels.
> +	 * McBSP3 as example again (16 or 32 bit samples):
> +	 * 1 channel (mono): size is 128 frames (128 words)
> +	 * 2 channels (stereo): size is 128 / 2 = 64 frames (2 * 64 words)
> +	 * 4 channels: size is 128 / 4 = 32 frames (4 * 32 words)
> +	 */
> +
> +	/*
> +	 * The first rule is for the buffer size, we should not allow smaller
> +	 * buffer than the FIFO size to avoid underruns
> +	 */
> +	snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
> +				    hw_rule_bsize_by_channels, mcbsp_data,
> +				    SNDRV_PCM_HW_PARAM_BUFFER_SIZE, -1);
> +

Obviously this hw_rule must be moved after checking the CPU type, since it is 
only valid for OMAP3 class of devices.
I'll fix this in the v2 series.
I have been testing this on OMAP3...

>  	if (cpu_is_omap343x()) {
>  		int dma_op_mode = omap_mcbsp_get_dma_op_mode(bus_id);
> -		int max_period;
> 
>  		/*
> -		 * McBSP2 in OMAP3 has 1024 * 32-bit internal audio buffer.
> -		 * Set constraint for minimum buffer size to the same than FIFO
> -		 * size in order to avoid underruns in playback startup because
> -		 * HW is keeping the DMA request active until FIFO is filled.
> +		 * In case os threshold mode, the rule will ensure, that the
> +		 * period size is not bigger than the maximum allowed threshold
> +		 * value.
>  		 */
> -		if (bus_id == 1)
> -			snd_pcm_hw_constraint_minmax(substream->runtime,
> -					SNDRV_PCM_HW_PARAM_BUFFER_BYTES,
> -					4096, UINT_MAX);
> -
> -		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
> -			max_period = omap_mcbsp_get_max_tx_threshold(bus_id);
> -		else
> -			max_period = omap_mcbsp_get_max_rx_threshold(bus_id);
> -
> -		max_period++;
> -		max_period <<= 1;
> -
>  		if (dma_op_mode == MCBSP_DMA_MODE_THRESHOLD)
> -			snd_pcm_hw_constraint_minmax(substream->runtime,
> -						SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
> -						32, max_period);
> +			snd_pcm_hw_rule_add(substream->runtime, 0,
> +					SNDRV_PCM_HW_PARAM_CHANNELS,
> +					hw_rule_psize_by_channels, substream,
> +					SNDRV_PCM_HW_PARAM_PERIOD_SIZE, -1);
>  	}
> 
>  	return err;

-- 
Péter