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SubjectRe: [PATCH v2] ASoC: atmel_ssc_dai: Allow more rates
Hi Peter,

On 02/04/2015 07:52 PM, Peter Rosin wrote:
> From: Peter Rosin <peda@axentia.se>
>
> When the SSC acts as BCK master, use a ratnum rule to limit
> the rate instead of only doing the standard rates. When the SSC
> acts as BCK slave, allow any BCK frequency up to within 500ppm
> of the SSC master clock, possibly divided by 2, 3 or 6.
>
> Put a cap at 384kHz. Who's /ever/ going to need more than that?
>
> The divider of 2, 3 or 6 is selected based on the Serial Clock Ratio
> Considerations section from the SSC documentation:
>
> The Transmitter and the Receiver can be programmed to operate
> with the clock signals provided on either the TK or RK pins.
> This allows the SSC to support many slave-mode data transfers.
> In this case, the maximum clock speed allowed on the RK pin is:
> - Peripheral clock divided by 2 if Receiver Frame Synchro is input
> - Peripheral clock divided by 3 if Receiver Frame Synchro is output
> In addition, the maximum clock speed allowed on the TK pin is:
> - Peripheral clock divided by 6 if Transmit Frame Synchro is input
> - Peripheral clock divided by 2 if Transmit Frame Synchro is output
>
> Signed-off-by: Peter Rosin <peda@axentia.se>
> ---
> sound/soc/atmel/atmel_ssc_dai.c | 113 +++++++++++++++++++++++++++++++++++++--
> sound/soc/atmel/atmel_ssc_dai.h | 1 +
> 2 files changed, 110 insertions(+), 4 deletions(-)
>
> Changes since v1:
>
> - I have checked all Atmel datasheets I could get my hands on (and
> that seemed relevant), and in every instance where they have
> described the SSC, the description have the exact rate limitations
> on the RK and TK pin that I have implemented here.
>
> - Improved the comments.
>
> - Rebased on top of the latest patches from Bo Chen.
>
> One thing remains a bit unclear, and that is the 500ppm deduction. Is
> that really warranted? The number was just pulled out of my hat...
>
> Cheers,
> Peter
>
> diff --git a/sound/soc/atmel/atmel_ssc_dai.c b/sound/soc/atmel/atmel_ssc_dai.c
> index 379ac2a6ab16..767f65bab25d 100644
> --- a/sound/soc/atmel/atmel_ssc_dai.c
> +++ b/sound/soc/atmel/atmel_ssc_dai.c
> @@ -187,6 +187,96 @@ static irqreturn_t atmel_ssc_interrupt(int irq, void *dev_id)
> return IRQ_HANDLED;
> }
>
> +/*
> + * When the bit clock is input, limit the maximum rate according to the
> + * Serial Clock Ratio Considerations section from the SSC documentation:
> + *
> + * The Transmitter and the Receiver can be programmed to operate
> + * with the clock signals provided on either the TK or RK pins.
> + * This allows the SSC to support many slave-mode data transfers.
> + * In this case, the maximum clock speed allowed on the RK pin is:
> + * - Peripheral clock divided by 2 if Receiver Frame Synchro is input
> + * - Peripheral clock divided by 3 if Receiver Frame Synchro is output
> + * In addition, the maximum clock speed allowed on the TK pin is:
> + * - Peripheral clock divided by 6 if Transmit Frame Synchro is input
> + * - Peripheral clock divided by 2 if Transmit Frame Synchro is output
> + *
> + * When the bit clock is output, limit the rate according to the
> + * SSC divider restrictions.
> + */
> +static int atmel_ssc_hw_rule_rate(struct snd_pcm_hw_params *params,
> + struct snd_pcm_hw_rule *rule)
> +{
> + struct atmel_ssc_info *ssc_p = rule->private;
> + struct ssc_device *ssc = ssc_p->ssc;
> + struct snd_interval *i = hw_param_interval(params, rule->var);
> + struct snd_interval t;
> + struct snd_ratnum r = {
> + .den_min = 1,
> + .den_max = 4095,
> + .den_step = 1,
> + };
> + unsigned int num = 0, den = 0;
> + int frame_size;
> + int mck_div = 2;
> + int ret;
> +
> + frame_size = snd_soc_params_to_frame_size(params);
> + if (frame_size < 0)
> + return frame_size;
> +
> + switch (ssc_p->daifmt & SND_SOC_DAIFMT_MASTER_MASK) {
> + case SND_SOC_DAIFMT_CBM_CFS:
> + if ((ssc_p->dir_mask & SSC_DIR_MASK_CAPTURE)
> + && ssc->clk_from_rk_pin)
> + /* Receiver Frame Synchro (i.e. capture)
> + * is output (format is _CFS) and the RK pin
> + * is used for input (format is _CBM_).
> + */
> + mck_div = 3;
> + break;
> +
> + case SND_SOC_DAIFMT_CBM_CFM:
> + if ((ssc_p->dir_mask & SSC_DIR_MASK_PLAYBACK)
> + && !ssc->clk_from_rk_pin)
> + /* Transmit Frame Synchro (i.e. playback)
> + * is input (format is _CFM) and the TK pin
> + * is used for input (format _CBM_ but not
> + * using the RK pin).
> + */
> + mck_div = 6;
> + break;
> + }
> +
> + switch (ssc_p->daifmt & SND_SOC_DAIFMT_MASTER_MASK) {
> + case SND_SOC_DAIFMT_CBS_CFS:
> + r.num = ssc_p->mck_rate / mck_div / frame_size;
> +
> + ret = snd_interval_ratnum(i, 1, &r, &num, &den);
> + if (ret >= 0 && den && rule->var == SNDRV_PCM_HW_PARAM_RATE) {
> + params->rate_num = num;
> + params->rate_den = den;
> + }
> + break;
> +
> + case SND_SOC_DAIFMT_CBM_CFS:
> + case SND_SOC_DAIFMT_CBM_CFM:
> + t.min = 8000;
> + t.max = ssc_p->mck_rate / mck_div / frame_size;
> + /* Take away 500ppm, just to be on the safe side. */
> + t.max -= t.max / 2000;
> + t.openmin = t.openmax = 0;
> + t.integer = 0;
> + ret = snd_interval_refine(i, &t);
> + break;
> +
> + default:
> + ret = -EINVAL;
> + break;
> + }
> +
> + return ret;
> +}
>
> /*-------------------------------------------------------------------------*\
> * DAI functions
> @@ -200,6 +290,7 @@ static int atmel_ssc_startup(struct snd_pcm_substream *substream,
> struct atmel_ssc_info *ssc_p = &ssc_info[dai->id];
> struct atmel_pcm_dma_params *dma_params;
> int dir, dir_mask;
> + int ret;
>
> pr_debug("atmel_ssc_startup: SSC_SR=0x%u\n",
> ssc_readl(ssc_p->ssc->regs, SR));
> @@ -207,6 +298,7 @@ static int atmel_ssc_startup(struct snd_pcm_substream *substream,
> /* Enable PMC peripheral clock for this SSC */
> pr_debug("atmel_ssc_dai: Starting clock\n");
> clk_enable(ssc_p->ssc->clk);
> + ssc_p->mck_rate = clk_get_rate(ssc_p->ssc->clk) * 2;

Why the mck_rate is calculated in this form?

> /* Reset the SSC to keep it at a clean status */
> ssc_writel(ssc_p->ssc->regs, CR, SSC_BIT(CR_SWRST));
> @@ -219,6 +311,17 @@ static int atmel_ssc_startup(struct snd_pcm_substream *substream,
> dir_mask = SSC_DIR_MASK_CAPTURE;
> }
>
> + ret = snd_pcm_hw_rule_add(substream->runtime, 0,
> + SNDRV_PCM_HW_PARAM_RATE,
> + atmel_ssc_hw_rule_rate,
> + ssc_p,
> + SNDRV_PCM_HW_PARAM_FRAME_BITS,
> + SNDRV_PCM_HW_PARAM_CHANNELS, -1);
> + if (ret < 0) {
> + dev_err(dai->dev, "Failed to specify rate rule: %d\n", ret);
> + return ret;
> + }
> +
> dma_params = &ssc_dma_params[dai->id][dir];
> dma_params->ssc = ssc_p->ssc;
> dma_params->substream = substream;
> @@ -783,8 +886,6 @@ static int atmel_ssc_resume(struct snd_soc_dai *cpu_dai)
> # define atmel_ssc_resume NULL
> #endif /* CONFIG_PM */
>
> -#define ATMEL_SSC_RATES (SNDRV_PCM_RATE_8000_96000)
> -
> #define ATMEL_SSC_FORMATS (SNDRV_PCM_FMTBIT_S8 | SNDRV_PCM_FMTBIT_S16_LE |\
> SNDRV_PCM_FMTBIT_S24_LE | SNDRV_PCM_FMTBIT_S32_LE)
>
> @@ -804,12 +905,16 @@ static struct snd_soc_dai_driver atmel_ssc_dai = {
> .playback = {
> .channels_min = 1,
> .channels_max = 2,
> - .rates = ATMEL_SSC_RATES,
> + .rates = SNDRV_PCM_RATE_CONTINUOUS,
> + .rate_min = 8000,
> + .rate_max = 384000,

Why this need to be changed? Do you mean in your application, the rates
will exceed 96000?

> .formats = ATMEL_SSC_FORMATS,},
> .capture = {
> .channels_min = 1,
> .channels_max = 2,
> - .rates = ATMEL_SSC_RATES,
> + .rates = SNDRV_PCM_RATE_CONTINUOUS,
> + .rate_min = 8000,
> + .rate_max = 384000,

Ditto.

> .formats = ATMEL_SSC_FORMATS,},
> .ops = &atmel_ssc_dai_ops,
> };
> diff --git a/sound/soc/atmel/atmel_ssc_dai.h b/sound/soc/atmel/atmel_ssc_dai.h
> index b1f08d511495..80b153857a88 100644
> --- a/sound/soc/atmel/atmel_ssc_dai.h
> +++ b/sound/soc/atmel/atmel_ssc_dai.h
> @@ -115,6 +115,7 @@ struct atmel_ssc_info {
> unsigned short rcmr_period;
> struct atmel_pcm_dma_params *dma_params[2];
> struct atmel_ssc_state ssc_state;
> + unsigned long mck_rate;
> };
>
> int atmel_ssc_set_audio(int ssc_id);
>

Best Regards,
Bo Shen


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