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Date:   Tue, 29 Mar 2022 13:58:23 +0530
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From:   Sameer Pujar <spujar@nvidia.com>
Subject: Re: [RFC PATCH v2 4/6] ASoC: soc-pcm: tweak DPCM BE hw_param() call
 order
To:     =?UTF-8?Q?Amadeusz_S=c5=82awi=c5=84ski?= 
        <amadeuszx.slawinski@linux.intel.com>, broonie@kernel.org,
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On 28-03-2022 20:41, Amadeusz Sławiński wrote:
> On 3/28/2022 8:14 AM, 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.
>
> Above sentence seems to suggest that consumer can set clock only after
> provider has started, but code in this patch seems to do it the other
> way around?
>
This patch makes provider calls to happen first.

>>
>> 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.
>>
>
> I'm bit confused by " With this hw_param() calls for provider BEs happen
> first and then followed by consumer BEs. "
>
> Aren't consumers started first and provider second? Code and previous
> sentence "connecting the provider BEs late to a FE" confuse me.

The dpcm_be_connect() call adds the new connection to a list using 
list_add() which would be a stack. When dpcm_be_connect() is deferred 
for provider BEs, these occupy top of the stack. When operating on this 
list during hw_params() stage, the provider call happen first. Is this 
part clear now? I can rephrase the comments/commit message for more clarity.

>
>
> Overall I don't exactly understand correct order of events after reading
> commit message and patch...
>
Consider there are two BEs (BE1 and BE2) and "BE1<==>BE2" can be an I2S 
interface for example. I am trying to get following sequence.

1. When BE1 is provider and BE2 is consumer, the call sequence expected 
is : hw_params(BE1) -> hw_params(BE2).

2. When BE2 is provider and BE1 is consumer, the call sequence expected 
is : hw_params(BE2) -> hw_params(BE1).

Idea is to make use of standard clock functions for rate info. Provider 
can use clk_set_rate() and consumer can clk_get_rate().

>> 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;
>> +
>> +     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
>
> Not sure about this define, it adds unnecessary limitation on max clock
> number, can't you just run same loop twice while checking
> defer_dpcm_be_connect() first time and !defer_dpcm_be_connect() second
> time? defer_dpcm_be_connect() function name may need a bit of adjustment
> (rtd_is_clock_consumer() maybe?), but it gets rid of the limit.
>
> or do something like following instead of copy pasting loop twice:
>
> rename original dpcm_add_paths() to _dpcm_add_paths() and add additional
> argument and check somewhere inline:
> static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream,
>        struct snd_soc_dapm_widget_list **list_, bool clock_consumer)
> {
>        ...
>
>  // with renamed defer_dpcm_be_connect
>        if (clock_consumer ^ !rtd_is_clock_consumer())
>                continue;
>
>        ...
> }
>
> static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream,
>        struct snd_soc_dapm_widget_list **list_)
> {
>        int ret;
>
>        /* start clock consumer BEs */
>        ret = _dpcm_add_paths(*fe, stream, **list_, true);
>        if (ret)
>                return ret;
>
>        /* start clock provider BEs */
>        ret = _dpcm_add_paths(*fe, stream, **list_, false);
>
>        return ret;
> }
>
Thanks for the suggestion. I will check if loop copy can be avoided.


>> +
>>   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) {
>> +                             dev_err(fe->dev, "ASoC: too many clock 
>> provider BEs\n");
>> +                             return -EINVAL;
>> +                     }
>> +
>> +                     prov[count++] = be;
>> +                     continue;
>> +             }
>> +
>> +             /* newly connected FE and BE */
>> +             err = dpcm_be_connect(fe, be, stream);
>> +             if (err < 0) {
>> +                     dev_err(fe->dev, "ASoC: can't connect %s\n",
>> +                             widget->name);
>> +                     break;
>> +             } else if (err == 0) /* already connected */
>> +                     continue;
>> +
>> +             /* new */
>> +             dpcm_set_be_update_state(be, stream, 
>> SND_SOC_DPCM_UPDATE_BE);
>> +             new++;
>> +     }
>> +
>> +     /*
>> +      * Now connect clock provider BEs. A late connection means,
>> +      * these BE links appear first in the list maintained by FE
>> +      * and hw_param() call for these happen first.
>
> Let's stick to ALSA terminology, hw_params() please, same in commit 
> message.

Sorry about this. I will fix it.