Re: [RFC PATCH v2 4/6] ASoC: soc-pcm: tweak DPCM BE hw_param() call order

On 28-03-2022 20:59, Ranjani Sridharan wrote:

On Mon, 2022-03-28 at 11:44 +0530, Sameer Pujar wrote:

...

For DPCM links, the order of hw_param() call depends on the sequence of BE connection to FE. It is possible that one BE link can provide clock to another BE link. In such cases consumer BE DAI, to get the rate set by provider BE DAI, can use the standard clock functions only if provider has already set the appropriate rate during its hw_param() stage.

Presently the order is fixed and does not depend on the provider and consumer relationships. So the clock rates need to be known ahead of hw_param() stage.

This patch tweaks the hw_param() order by connecting the provider BEs late to a FE. With this hw_param() calls for provider BEs happen first and then followed by consumer BEs. The consumers can use the standard clk_get_rate() function to get the rate of the clock they depend on.

Signed-off-by: Sameer Pujarspujar@nvidia.com

TODO:

• The FE link is not considered in this. For Tegra it is fine to call hw_params() for FE at the end. But systems, which want to

apply this tweak for FE as well, have to extend this tweak to FE.

• Also only DPCM is considered here. If normal links require such tweak, it needs to be extended.

sound/soc/soc-pcm.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c index 9a95468..5829514 100644 --- a/sound/soc/soc-pcm.c +++ b/sound/soc/soc-pcm.c @@ -1442,6 +1442,29 @@ static int dpcm_prune_paths(struct snd_soc_pcm_runtime *fe, int stream, return prune; }

+static bool defer_dpcm_be_connect(struct snd_soc_pcm_runtime *rtd) +{

• struct snd_soc_dai *dai;
  

• int i;
  

• if (!(rtd->dai_link->dai_fmt & SND_SOC_DAIFMT_FORMAT_MASK))
  

•         return false;
  

Is this check necessary?

By default the link has "SND_SOC_DAIFMT_CBC_CFC". When no format (I2S/RIGHT_J etc.,) is specified, the links are mostly internal and the normal order can be followed.

...

• if ((rtd->dai_link->dai_fmt &
  

SND_SOC_DAIFMT_CLOCK_PROVIDER_MASK) ==

•     SND_SOC_DAIFMT_CBC_CFC) {
  

•         for_each_rtd_cpu_dais(rtd, i, dai) {
  

•                 if (!snd_soc_dai_is_dummy(dai))
  

•                         return true;
  

•         }
  

• }
  

• return false;
  

+}

+#define MAX_CLK_PROVIDER_BE 10

• static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int

stream, struct snd_soc_dapm_widget_list **list_) { @@ -1449,7 +1472,8 @@ static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream, struct snd_soc_dapm_widget_list *list = *list_; struct snd_soc_pcm_runtime *be; struct snd_soc_dapm_widget *widget;

• int i, new = 0, err;
  

• struct snd_soc_pcm_runtime *prov[MAX_CLK_PROVIDER_BE];
  

• int i, new = 0, err, count = 0;
  
   /* Create any new FE <--> BE connections */
   for_each_dapm_widgets(list, i, widget) {
  

@@ -1489,6 +1513,40 @@ static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream, (be->dpcm[stream].state != SND_SOC_DPCM_STATE_CLOSE)) continue;

•         /* Connect clock provider BEs at the end */
  

•         if (defer_dpcm_be_connect(be)) {
  

•                 if (count >= MAX_CLK_PROVIDER_BE) {
  

What determines MAX_CLK_PROVIDER_BE? why 10? Can you use rtd->num_cpus instead?

There is no specific reason as why it cannot be more than 10. I mostly thought it would be a fair assumption to have these many clock providers for audio paths. I will check if such limitation can be avoided. I cannot rely on "rtd->num_cpus", since in my case there are two different rtds one acting as provider and other as consumer.