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

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;