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

Sameer Pujar
2022-03-29T08:31:38Z

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 Pujar<spujar@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.