ALSA: firewire-lib: tune the maximum available size of PCM period

					struct snd_pcm_runtime *runtime)

{

	struct snd_pcm_hardware *hw = &runtime->hw;

	unsigned int ctx_header_size;

	unsigned int maximum_usec_per_period;

	int err;

	hw->info = SNDRV_PCM_INFO_BATCH |

	hw->period_bytes_max = hw->period_bytes_min * 2048;

	hw->buffer_bytes_max = hw->period_bytes_max * hw->periods_min;

	/*

	 * Currently firewire-lib processes 16 packets in one software

	 * interrupt callback. This equals to 2msec but actually the

	 * interval of the interrupts has a jitter.

	 * Additionally, even if adding a constraint to fit period size to

	 * 2msec, actual calculated frames per period doesn't equal to 2msec,

	 * depending on sampling rate.

	 * Anyway, the interval to call snd_pcm_period_elapsed() cannot 2msec.

	 * Here let us use 5msec for safe period interrupt.

	 */

	// Linux driver for 1394 OHCI controller voluntarily flushes isoc

	// context when total size of accumulated context header reaches

	// PAGE_SIZE. This kicks tasklet for the isoc context and brings

	// callback in the middle of scheduled interrupts.

	// Although AMDTP streams in the same domain use the same events per

	// IRQ, use the largest size of context header between IT/IR contexts.

	// Here, use the value of context header in IR context is for both

	// contexts.

	if (!(s->flags & CIP_NO_HEADER))

		ctx_header_size = IR_CTX_HEADER_SIZE_CIP;

	else

		ctx_header_size = IR_CTX_HEADER_SIZE_NO_CIP;

	maximum_usec_per_period = USEC_PER_SEC * PAGE_SIZE /

				  CYCLES_PER_SECOND / ctx_header_size;

	err = snd_pcm_hw_constraint_minmax(runtime,

					   SNDRV_PCM_HW_PARAM_PERIOD_TIME,

					   5000, UINT_MAX);

					   5000, maximum_usec_per_period);

	if (err < 0)

		goto end;