Re: [PATCH v2 1/2] ASoC: fsl_asrc: make sure the input and output clocks are different

[Nicolin Chen <nicoleotsuka@gmail.com>]

On Thu, Jul 16, 2020 at 05:13:52PM +0200, Arnaud Ferraris wrote:
> The current clock selection algorithm might select the same clock for
> both input and output. This can happen when, for instance, the output
> sample rate is a multiple of the input rate.

What's the issue when selecting the same clock source for both
input and output? Please explain it in the commit logs.

> This patch makes sure it always selects distinct input and output
> clocks.
> 
> Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>
> ---
>  sound/soc/fsl/fsl_asrc.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/sound/soc/fsl/fsl_asrc.c b/sound/soc/fsl/fsl_asrc.c
> index 02c81d2e34ad..6d43cab6c885 100644
> --- a/sound/soc/fsl/fsl_asrc.c
> +++ b/sound/soc/fsl/fsl_asrc.c
> @@ -608,8 +608,8 @@ static void fsl_asrc_select_clk(struct fsl_asrc_priv *asrc_priv,
>  {
>  	struct fsl_asrc_pair_priv *pair_priv = pair->private;
>  	struct asrc_config *config = pair_priv->config;
> -	int rate[2], select_clk[2]; /* Array size 2 means IN and OUT */
> -	int clk_rate, clk_index;
> +	int rate[2], select_clk[2], clk_index[2]; /* Array size 2 means IN and OUT */
> +	int clk_rate;
>  	int i = 0, j = 0;
>  
>  	rate[IN] = in_rate;
> @@ -618,11 +618,12 @@ static void fsl_asrc_select_clk(struct fsl_asrc_priv *asrc_priv,
>  	/* Select proper clock source for internal ratio mode */
>  	for (j = 0; j < 2; j++) {
>  		for (i = 0; i < ASRC_CLK_MAP_LEN; i++) {
> -			clk_index = asrc_priv->clk_map[j][i];
> -			clk_rate = clk_get_rate(asrc_priv->asrck_clk[clk_index]);
> +			clk_index[j] = asrc_priv->clk_map[j][i];
> +			clk_rate = clk_get_rate(asrc_priv->asrck_clk[clk_index[j]]);
>  			/* Only match a perfect clock source with no remainder */

Better to update the comments here as there's a new condition.

>  			if (clk_rate != 0 && (clk_rate / rate[j]) <= 1024 &&
> -			    (clk_rate % rate[j]) == 0)
> +			    (clk_rate % rate[j]) == 0 &&
> +			    (j == 0 || clk_index[j] != clk_index[j-1]))

clk_index[j - 1]