question at am335x_iis_serializer_direction and snd_platform_data am335x_evm_snd_data

Hi Sir, 

Regard to below code, where can I find the document to talk about this?

or where can I find the usage about the structure?

I only can find some reference code in internet, sometimes am335x_evm_sk_iis_serializer_direction1[0]=RX_MODE, sometimes [3]

And about the snd_platform_data am335x_evm_sk_snd_data1 structure, some reference set: txnumevt=1 and rxnumevt=1, why?

======================================================================================

static u8 am335x_iis_serializer_direction1[] = {
	INACTIVE_MODE,	INACTIVE_MODE,	TX_MODE,	RX_MODE,
	INACTIVE_MODE,	INACTIVE_MODE,	INACTIVE_MODE,	INACTIVE_MODE,
	INACTIVE_MODE,	INACTIVE_MODE,	INACTIVE_MODE,	INACTIVE_MODE,
	INACTIVE_MODE,	INACTIVE_MODE,	INACTIVE_MODE,	INACTIVE_MODE,
};

static struct snd_platform_data am335x_evm_snd_data1 = {
	.tx_dma_offset	= 0x46400000,	/* McASP1 */
	.rx_dma_offset	= 0x46400000,
	.op_mode	= DAVINCI_MCASP_IIS_MODE,
	.num_serializer	= ARRAY_SIZE(am335x_iis_serializer_direction1),
	.tdm_slots	= 2,
	.serial_dir	= am335x_iis_serializer_direction1,
	.asp_chan_q	= EVENTQ_2,
	.version	= MCASP_VERSION_3,
	.txnumevt	= 32,
	.rxnumevt	= 32,
	.get_context_loss_count	=
			omap_pm_get_dev_context_loss_count,
};
===========================================================================