Re: [PATCH 1/3] ASoC: omap-mcbsp: Fix latency value calculation for pm_qos

From: Peter Ujfalusi <peter.ujfalusi@ti.com>
To: Jarkko Nikula <jarkko.nikula@bitmer.com>,
	Mark Brown <broonie@kernel.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	tony@atomide.com
Cc: kernel@pyra-handheld.com, hns@goldelico.com,
	alsa-devel@alsa-project.org, linux-omap@vger.kernel.org,
	matt@ranostay.consulting
Subject: Re: [PATCH 1/3] ASoC: omap-mcbsp: Fix latency value calculation for pm_qos
Date: Mon, 19 Nov 2018 16:14:13 +0200	[thread overview]
Message-ID: <c26c055f-5f7a-46b5-a409-6b60f0657f56@ti.com> (raw)
In-Reply-To: <d1e6e9df-3893-7c2d-acbb-05b59011a364@bitmer.com>

On 2018-11-18 19:04, Jarkko Nikula wrote:
> On 11/14/18 1:06 PM, Peter Ujfalusi wrote:
>> The latency number is in usec for the pm_qos. Correct the calculation to
>> give us the time in usec
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
>> ---
>>  sound/soc/omap/omap-mcbsp.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/sound/soc/omap/omap-mcbsp.c b/sound/soc/omap/omap-mcbsp.c
>> index e0ef4774c710..a395598f1f20 100644
>> --- a/sound/soc/omap/omap-mcbsp.c
>> +++ b/sound/soc/omap/omap-mcbsp.c
>> @@ -999,9 +999,9 @@ static int omap_mcbsp_dai_hw_params(struct snd_pcm_substream *substream,
>>  			pkt_size = channels;
>>  		}
>>  
>> -		latency = ((((buffer_size - pkt_size) / channels) * 1000)
>> -				 / (params->rate_num / params->rate_den));
>> -
>> +		latency = (buffer_size - pkt_size) / channels;
>> +		latency = latency * USEC_PER_SEC /
>> +			  (params->rate_num / params->rate_den);
> 
> Did I understand correctly this doesn't fix any audio issue but allows
> CPU sleep longer or reach deeper sleep?

PM core will block any power state from where the wake-up would take
longer than the latency value.

The latency is in usec, this patch just fixing the calculation to get
the time in usec.

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
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