linux-kernel - Re: [PATCH v2 3/3] ASoC: fsl_sai: Fix TCSR.TE/RCSR.RE in synchronous mode

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Message-ID: <20190916231115.GD12789@Asurada-Nvidia.nvidia.com>
Date:   Mon, 16 Sep 2019 16:11:15 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Daniel Baluta <daniel.baluta@....com>
Cc:     broonie@...nel.org, timur@...nel.org, Xiubo.Lee@...il.com,
        festevam@...il.com, lgirdwood@...il.com, perex@...ex.cz,
        tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, NXP Linux Team <linux-imx@....com>
Subject: Re: [PATCH v2 3/3] ASoC: fsl_sai: Fix TCSR.TE/RCSR.RE in synchronous
 mode

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