[alsa-devel] [PATCH 2/2] ASoC: fsl_ssi: Fix number of words per frame for I2S-slave mode

[Nicolin Chen]

On Sat, Jun 25, 2016 at 07:59:22AM +0300, Alexander Shiyan wrote:
> The i.MX51 datasheet says:
> Chapter 56.1.2.4 I2S Mode
> ...
> When I2S modes are entered (I2S master (01) or I2S slave (10)),
> the following settings are recommended:
> ...
> - TX Frame Rate should be 2 i.e. (STCCR[12:8] = 1)
> - RX Frame Rate should be 2 i.e. (SRCCR[12:8] = 1)
> 
> Chapter 56.3.3.12 SSI Transmit and Receive Clock Control Registers (STCCR & SRCCR)
> ...
> Bits 12-8 DC4-DC0
> Frame Rate Divider Control. These bits are used to control the divide ratio
> for the programmable frame rate dividers. The divide ratio works on the word
> clock. In Normal mode, this ratio determines the word transfer rate.
> In Network mode, this ratio sets the number of words per frame. The divide
> ratio ranges from 1 to 32 in Normal mode and from 2 to 32 in Network mode.
> In Normal mode, a divide ratio of 1 (DC=00000) provides continuous periodic
> data word transfer. A bit-length frame sync must be used in this case.
> 
> Function fsl_ssi_hw_params() setup Normal mode for MONO output,
> so with DC=0, SSI enters to continuous periodic data word transfer.
> To fix this, setup DC for any I2S mode.

The change looks fine and didn't show any problem when I tested it.
But I am wondering what's the failed user case here so we need this
patch to fix? (The mono playback works without this patch as well.)

Thanks
Nicolin