[alsa-devel] Question about snd_pcm_limit_hw_rates() call timing

[Kuninori Morimoto]

Hi ALSA ML

soc-pcm has snd_pcm_limit_hw_rates() which determine rate_min/rate_max fields.
It updates runtime->hw.rate_min/max (A) based on hw->rates (B).

	int snd_pcm_limit_hw_rates(struct snd_pcm_runtime *runtime)
	{
		int i;
		for (i = 0; i < (int)snd_pcm_known_rates.count; i++) {
(B)			if (runtime->hw.rates & (1 << i)) {
(A)				runtime->hw.rate_min = snd_pcm_known_rates.list[i];
				break;
			}
		}
		for (i = (int)snd_pcm_known_rates.count - 1; i >= 0; i--) {
(B)			if (runtime->hw.rates & (1 << i)) {
(A)				runtime->hw.rate_max = snd_pcm_known_rates.list[i];
				break;
			}
		}
		return 0;
	}

I guess the calling timing is

	1) set hw->rates
	2) call snd_pcm_limit_hw_rates()
	3) update hw->rate_min/max

soc_pcm_init_runtime_hw() is calling it as this order

	static void soc_pcm_init_runtime_hw(xxx)
	{
		...
1)		hw->rates = snd_pcm_rate_mask_intersect(rates, cpu_stream->rates);

2)		snd_pcm_limit_hw_rates(runtime);

3)		hw->rate_min = max(hw->rate_min, cpu_stream->rate_min);
		hw->rate_min = max(hw->rate_min, rate_min);
		hw->rate_max = min_not_zero(hw->rate_max, cpu_stream->rate_max);
		hw->rate_max = min_not_zero(hw->rate_max, rate_max);
	}

But, dpcm_fe_dai_startup() are different.

	static int dpcm_fe_dai_startup(xxx)
	{
		...
		/*
		 * dpcm_set_fe_runtime() updates runtime->hw.xxx
		 */
1) 3)		dpcm_set_fe_runtime(fe_substream);
2)		snd_pcm_limit_hw_rates(runtime);
		...
	}

I guess we need fixup dpcm_fe_dai_startup() ?

Thank you for your help !!
Best regards
---
Kuninori Morimoto