linux-kernel - Re: [PATCH v2 1/1] ASoC: fsl_ssi: add CCSR_SSI

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Date:	Thu, 28 Apr 2016 20:45:02 -0700
From:	Nicolin Chen <nicoleotsuka@...il.com>
To:	Caleb Crome <caleb@...me.org>
Cc:	Timur Tabi <timur@...i.org>, Xiubo Li <Xiubo.Lee@...il.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] ASoC: fsl_ssi: add CCSR_SSI_SOR to volatile
 register list

On Mon, Apr 25, 2016 at 11:36:18AM -0700, Caleb Crome wrote:
> The CCSR_SSI_SOR is a register that clears the TX and/or the RX fifo
> on the i.MX SSI port.  The fsl_ssi_trigger writes this register in
> order to clear the fifo at trigger time.
> 
> However, since the CCSR_SSI_SOR register is not in the volatile list,
> the caching mechanism prevented the register write in the trigger
> function.  This caused the fifo to not be cleared (because the value
> was unchanged from the last time the register was written), and thus
> causes the channels in both TDM or simple I2S mode to slip and be in
> the wrong time slots on SSI restart.
> 
> This has gone unnoticed for so long because with simple stereo mode,
> the consequence is that left and right are swapped, which isn't that
> noticeable.  However, it's catestrophic in some systems that
> require the channels to be in the right slots.
> 
> Signed-off-by: Caleb Crome <caleb@...me.org>
> Suggested-by: Arnaud Mouiche <arnaud.mouiche@...oxia.com>

Acked-by: Nicolin Chen <nicoleotsuka@...il.com>

Thanks

> 
> ---
>  sound/soc/fsl/fsl_ssi.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
> index 216e3cb..2f3bf9c 100644
> --- a/sound/soc/fsl/fsl_ssi.c
> +++ b/sound/soc/fsl/fsl_ssi.c
> @@ -151,6 +151,7 @@ static bool fsl_ssi_volatile_reg(struct device *dev, unsigned int reg)
>  	case CCSR_SSI_SACDAT:
>  	case CCSR_SSI_SATAG:
>  	case CCSR_SSI_SACCST:
> +	case CCSR_SSI_SOR:
>  		return true;
>  	default:
>  		return false;
> -- 
> 1.9.1
>