On 12/09/2017 23:32, Nicolin Chen wrote:
On Tue, Sep 12, 2017 at 04:35:13PM +0200, Arnaud Mouiche wrote:
- * freq: Output BCLK frequency = samplerate * 32 (fixed) * channels
- * dir: SND_SOC_CLOCK_OUT -> TxBCLK, SND_SOC_CLOCK_IN -> RxBCLK.
+ * freq: Output BCLK frequency = samplerate * 32 (fixed) * slots (or channels)
Slots are not necessarily 32 bits width.
Indeed, a simple grep of snd_soc_dai_set_tdm_slot shows 16, 24, 32
and 0 bits usage. (don't know the real meaning of 0 BTW...)
So, it should be good to also remember the slots width given in
snd_soc_dai_set_tdm_slot() call.
RM says that the word length is fixed to 32 in I2S Master mode.
So I used it here. But I think using it with the slots could be
wrong here as you stated. What kind of clock rates (bit and lr)
does a TDM case have?
The problem of slot width here is handled in the set_tdm_slot()
at all. So I tried to ignored that. But we probably do need it
when calculating things with the slot number.
Could you please give me a few set of examples of how you set
set_sysclk(), set_tdm_slot() with the current driver? The idea
here is to figure out a way to calculate the bclk in hw_params
without getting set_sysclk() involved any more.
Here is one, where a bclk = 4*16*fs is expected
static int imx_hifi_hw_params(struct snd_pcm_substream *substream,
struct snd_pcm_hw_params *params)
{
struct snd_soc_pcm_runtime *rtd = substream->private_data;
struct imx_priv *priv = &card_priv;
struct device *dev = &priv->pdev->dev;
int ret = 0;
struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
unsigned int freq;
int ch;
/* configuring cpu_dai
* - bitclk (fclk is computed automatically)
* 16bit * 4 (max) channels * sampling rate
* - tdm maskto select the active channels
*/
freq = 4 * 16 * params_rate(params);
if (freq != priv->current_freq) {
/* clk_id and direction are not taken in count by fsl_ssi
driver */
ret = snd_soc_dai_set_sysclk( cpu_dai, 0, freq, 0 );
if (ret) {
dev_err(dev, "failed to set cpu dai bitclk: %u\n", freq);
return ret;
}
priv->current_freq = freq;
}
ch = params_channels(params);
if (ch != priv->current_ch) {
ret = snd_soc_dai_set_tdm_slot( cpu_dai, (1 << ch)-1, (1 <<
ch)-1, 4, 16 );
if (ret) {
dev_err(dev, "failed to set cpu dai tdm slots:
ch=%d\n", ch);
return ret;
}
priv->current_ch = ch;
}
return 0;
}
In another setup, there are 8 x 16 bits slots, whatever the number of
active channels is.
In this case bclk = 128 * fs
The number of slots is completely arbitrary. Some slots can even be
reserved for communication between codecs that don't communicate with linux.
Anyway, there is something wrong in the snd_soc_codec_set_sysclk
usage by fsl_ssi
Let's get a look again at the description:
/**
* snd_soc_dai_set_sysclk - configure DAI system or master clock.
* @dai: DAI
* @clk_id: DAI specific clock ID
* @freq: new clock frequency in Hz
* @dir: new clock direction - input/output.
*
* Configures the DAI master (MCLK) or system (SYSCLK) clocking.
*/
int snd_soc_dai_set_sysclk(struct snd_soc_dai *dai, int clk_id,
unsigned int freq, int dir)
So, it can be used to configure 2 different clocks (and more) with
different usages.
Lukasz complains that simple-card is configuring MCLK incorrectly.
but simple-card, only want to configure the SYSCLK, whereas fsl_ssi
understand "configure the MCLK..." (fsl_ssi doesn't check the clk_id
at all)
It's more than a clock_id in my opinion. The driver now sets
the bit clock rate via set_sysclk() other than the MCLK rate
actually.
I think the problem is here.
I would propose a new clk_id
#define FSL_SSI_SYSCLK_MCLK 1
And leave fsl_ssi_set_dai_sysclk(xxx, FSL_SSI_SYSCLK_MCLK, ...)
override the computed mlck.
This will leave a way for obscure TDM users to specify a specific a
random mclk frequency for obscure reasons...
Unfortunately, such generic clock_id (sysclk, mclk) were never
defined widely.
Unfortunately, it looks like a work around to me. I understand
the idea of leaving set_sysclk() out there to override the bit
clock is convenient, but it is not a standard ALSA design and
may eventually introduce new problems like today.
I agree. I'm not conservative at all concerning this question.
I don't see a way to remove set_sysclk without breaking current TDM
users anyway, at least for those who don't have their code upstreamed.
All information provided through snd_soc_dai_set_tdm_slot( cpu_dai,
mask, mask, slots, width ) should be enough
In this case, for TDM users
bclk = slots * width * fs (where slots is != channels)
will manage 99 % of the cases.
And the remaining 1% will concern people who need to hack the kernel so
widely they don't care about the set_sysclk removal.
Now, looking at the code currently in linus/master:sound/soc/fsl
concerning TDM
- imx-mc13783.c : the codec is master => OK
- fsl-asoc-card.c : *something will break since snd_soc_dai_set_sysclk
returned code is checked*
- eukrea-tlv320.c : based on imx-ssi.c, so not affected by changes in
fsl_ssi.c. Use set_sysclk() only to setup the clock direction
- wm1133-ev1.c : bclk generated by the codec. set_sysclk() not called
for cpu_dai
Consequently, we can say that few things is broken in linux upstream if
set_sysclk is removed, and this can be fixed easily for fsl-asoc-card.c
Arnaud
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