[PATCH v3 1/1] ASoC: fsl_asrc: make sure the input and output clocks are different

[Nicolin Chen]

On Fri, Jul 17, 2020 at 12:38:58PM +0200, Arnaud Ferraris wrote:
> The current clock selection algorithm might select the same clock for
> both input and output when, for instance, the output sample rate is a
> multiple of the input rate.
> 
> In that case, both selectable clocks will be multiples of both the input
> and output sample rates, and therefore the first of these clocks will be
> selected for both input and output, leading to miscalculation of the
> dividers for either the input or output side.
> 
> Example:
>   Input uses clock A (512kHz) and has a sample rate of 8kHz
>   Output uses clock B (1024kHz) and has a sample rate of 16kHz
> 
>   In this case, the algorithm will select clock A for both input and
>   output: the input divider will therefore be calculated properly
>   (512 / 8 => 64), but the output divider's value will be only half
>   the expected value (512 / 16 => 32 instead of 1024 / 16 => 64).
> 
> This patch makes sure it always selects distinct input and output
> clocks.

Please allow me to take some time to review the use case and
the changes. And I'd love to wait for a review from Shengjiu
also, as he introduced this auto-selection function and he's
more familiar with internal ratio mode.

Thanks

> Signed-off-by: Arnaud Ferraris <arnaud.ferraris at collabora.com>
> ---
>  sound/soc/fsl/fsl_asrc.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/sound/soc/fsl/fsl_asrc.c b/sound/soc/fsl/fsl_asrc.c
> index 02c81d2e34ad..de10c208d3c8 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 +618,15 @@ 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]);
> -			/* Only match a perfect clock source with no remainder */
> +			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
> +			 * and make sure the input & output clocks are different
> +			 */
>  			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]))
>  				break;
>  		}
>  
> -- 
> 2.27.0
>