[alsa-devel] [PATCH v2 3/3] ASoC: fsl_sai: Fix TCSR.TE/RCSR.RE in synchronous mode

[Nicolin Chen]

Hello Daniel,

On Fri, Sep 13, 2019 at 10:28:07PM +0300, Daniel Baluta wrote:
> The SAI transmitter and receiver can be configured to operate with
> synchronous bit clock and frame sync.
> 
> When Tx is synchronous with receiver RCSR.RE should be set in playback
> to enable the receiver which provides bit clock and frame sync.
> 
> When Rx is synchronous with transmitter TCSR.TE should be set in record
> to enable the transmitter which provides bit clock and frame sync.

I don't quite get what this patch fixes....can you explain?

> @@ -539,8 +539,8 @@ static int fsl_sai_trigger(struct snd_pcm_substream *substream, int cmd,
>  			   sai->synchronous[RX] ? FSL_SAI_CR2_SYNC : 0);
>  
>  	/*
> -	 * It is recommended that the transmitter is the last enabled
> -	 * and the first disabled.

This is copied from iMX6SX Reference Manual, IIRC...And I just
took a look at iMX8DXP/QXP RM: it has the exact same statement
in "16.16.3.3.1 Synchronous mode" section.

> +	 * it is recommended that the asynchronous block to be the last enabled
> +	 * and the first disabled

So... why are we changing to this? Any update/explain?

Thank you