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From: Takashi Iwai <tiwai@suse.de>
To: Stefan Wahren <stefan.wahren@i2se.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Eric Anholt <eric@anholt.net>,
	linux-rpi-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, Phil Elwell <phil@raspberrypi.org>
Subject: Re: [PATCH 17/29] staging: bcm2835-audio: Add 10ms period constraint
Date: Wed, 19 Sep 2018 11:52:33 +0200
Message-ID: <s5h4lelu84e.wl-tiwai@suse.de> (raw)
In-Reply-To: <4c5f9aed-8fbe-fe22-0c8d-097d8915805c@i2se.com>

On Wed, 19 Sep 2018 11:42:22 +0200,
Stefan Wahren wrote:
> 
> Hi Takashi,
> 
> Am 04.09.2018 um 17:58 schrieb Takashi Iwai:
> > It seems that the resolution of vc04 callback is in 10 msec; i.e. the
> > minimal period size is also 10 msec.
> >
> > This patch adds the corresponding hw constraint.
> >
> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > ---
> >  drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> > index 9659c25b9f9d..6d89db6e14e4 100644
> > --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> > +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> > @@ -145,6 +145,11 @@ static int snd_bcm2835_playback_open_generic(
> >  				   SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
> >  				   16);
> >  
> > +	/* position update is in 10ms order */
> > +	snd_pcm_hw_constraint_minmax(runtime,
> > +				     SNDRV_PCM_HW_PARAM_PERIOD_TIME,
> > +				     10 * 1000, UINT_MAX);
> > +
> >  	chip->alsa_stream[idx] = alsa_stream;
> >  
> >  	chip->opened |= (1 << idx);
> 
> in the Foundation Kernel (Downstream) there is a patch to interpolate
> the audio delay. So my questions is, does your patch above makes the
> following patch obsolete?

Through a quick glance, no, my patch is orthogonal to this.

My patch adds a PCM hw constraint so that the period size won't go
below 10ms, while the downstream patch provides the additional delay
value that is calculated from the system clock.

> [PATCH] bcm2835: interpolate audio delay
> 
> It appears the GPU only sends us a message all 10ms to update
> the playback progress. Other than this, the playback position
> (what SNDRV_PCM_IOCTL_DELAY will return) is not updated at all.
> Userspace will see jitter up to 10ms in the audio position.
> 
> Make this a bit nicer for userspace by interpolating the
> position using the CPU clock.
> 
> I'm not sure if setting snd_pcm_runtime.delay is the right
> approach for this. Or if there is maybe an already existing
> mechanism for position interpolation in the ALSA core.

That's OK, as long as the computation is accurate enough (at least not
exceed the actual position) and is light-weight.

> I only set SNDRV_PCM_INFO_BATCH because this appears to remove
> at least one situation snd_pcm_runtime.delay is used, so I have
> to worry less in which place I have to update this field, or
> how it interacts with the rest of ALSA.

Actually, this SNDRV_PCM_INFO_BATCH addition should be a separate
patch.  It has nothing to do with the runtime->delay calculation.
(And, this "one situation" is likely called PulseAudio :)

> In the future, it might be nice to use VC_AUDIO_MSG_TYPE_LATENCY.
> One problem is that it requires sending a videocore message, and
> waiting for a reply, which could make the implementation much
> harder due to locking and synchronization requirements.

This can be now easy with my patch series.  By switching to non-atomic
operation, we can issue the vc04 command inside the pointer callback,
too.


thanks,

Takashi

  reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-04 15:58 [PATCH 00/29] staging: bcm2835-audio: Cleanups and fixes Takashi Iwai
2018-09-04 15:58 ` [PATCH 01/29] staging: bcm2835-audio: Clean up mutex locks Takashi Iwai
2018-09-04 15:58 ` [PATCH 02/29] staging: bcm2835-audio: Remove redundant spdif stream ctls Takashi Iwai
2018-09-04 15:58 ` [PATCH 03/29] staging: bcm2835-audio: Clean up include files in bcm2835-ctl.c Takashi Iwai
2018-09-08 13:25   ` Stefan Wahren
2018-09-08 16:21     ` Takashi Iwai
2018-09-04 15:58 ` [PATCH 04/29] staging: bcm2835-audio: Remove redundant substream mask checks Takashi Iwai
2018-09-04 15:58 ` [PATCH 05/29] staging: bcm2835-audio: Fix mute controls, volume handling cleanup Takashi Iwai
2018-09-04 15:58 ` [PATCH 06/29] staging: bcm2835-audio: Remove redundant function calls Takashi Iwai
2018-09-04 15:58 ` [PATCH 07/29] staging: bcm2835-audio: Remove superfluous open flag Takashi Iwai
2018-09-04 15:58 ` [PATCH 08/29] staging: bcm2835-audio: Drop useless running flag and check Takashi Iwai
2018-09-04 15:58 ` [PATCH 09/29] staging: bcm2835-audio: Fix incorrect draining handling Takashi Iwai
2018-09-04 15:58 ` [PATCH 10/29] staging: bcm2835-audio: Kill unused spinlock Takashi Iwai
2018-09-04 15:58 ` [PATCH 11/29] staging: bcm2835-audio: Use PCM runtime values instead Takashi Iwai
2018-09-04 15:58 ` [PATCH 12/29] staging: bcm2835-audio: Drop unnecessary pcm indirect setup Takashi Iwai
2018-09-04 15:58 ` [PATCH 13/29] staging: bcm2835-audio: Drop useless NULL check Takashi Iwai
2018-09-04 15:58 ` [PATCH 14/29] staging: bcm2835-audio: Propagate parameter setup error Takashi Iwai
2018-09-04 15:58 ` [PATCH 15/29] staging: bcm2835-audio: Drop debug messages in bcm2835-pcm.c Takashi Iwai
2018-09-04 15:58 ` [PATCH 16/29] staging: bcm2835-audio: Drop superfluous mutex lock during prepare Takashi Iwai
2018-09-08 13:40   ` Stefan Wahren
2018-09-08 16:12     ` Takashi Iwai
2018-09-04 15:58 ` [PATCH 17/29] staging: bcm2835-audio: Add 10ms period constraint Takashi Iwai
2018-09-19  9:42   ` Stefan Wahren
2018-09-19  9:52     ` Takashi Iwai [this message]
2018-09-19 12:41       ` Stefan Wahren
2018-09-19 12:47         ` Mike Brady
2018-09-19 18:39         ` Takashi Iwai
2018-10-09 13:18           ` [PATCH 17/29] staging: bcm2835-audio: Add 10ms period constraint [Resend in plain text...] Mike Brady
2018-10-09 13:44             ` Takashi Iwai
2018-10-09 15:28               ` Mike Brady
2018-10-09 15:32                 ` Takashi Iwai
2018-10-11 12:53                 ` Mike Brady
2018-10-11 14:07                   ` Stefan Wahren
2018-10-13 15:00                   ` Mike Brady
2018-10-13 15:45                     ` Takashi Iwai
2018-09-04 15:58 ` [PATCH 18/29] staging: bcm2835-audio: Make single vchi handle Takashi Iwai
2018-09-04 15:58 ` [PATCH 19/29] staging: bcm2835-audio: Code refactoring of vchiq accessor codes Takashi Iwai
2018-09-04 15:58 ` [PATCH 20/29] staging: bcm2835-audio: Operate non-atomic PCM ops Takashi Iwai
2018-09-04 15:58 ` [PATCH 21/29] staging: bcm2835-audio: Use card->private_data Takashi Iwai
2018-09-04 15:58 ` [PATCH 22/29] staging: bcm2835-audio: Use standard error print helpers Takashi Iwai
2018-09-04 15:58 ` [PATCH 23/29] staging: bcm2835-audio: Remove unnecessary header file includes Takashi Iwai
2018-09-04 15:58 ` [PATCH 24/29] staging: bcm2835-audio: Move module parameter description Takashi Iwai
2018-09-04 15:58 ` [PATCH 25/29] staging: bcm2835-audio: Use coherent device buffers Takashi Iwai
2018-09-04 15:58 ` [PATCH 26/29] staging: bcm2835-audio: Set SNDRV_PCM_INFO_SYNC_APPLPTR Takashi Iwai
2018-09-04 15:58 ` [PATCH 27/29] staging: bcm2835-audio: Simplify PCM creation helpers Takashi Iwai
2018-09-04 15:58 ` [PATCH 28/29] staging: bcm2835-audio: Simplify kctl " Takashi Iwai
2018-09-04 15:58 ` [PATCH 29/29] staging: bcm2835-audio: Simplify card object management Takashi Iwai
2018-09-08 13:18 ` [PATCH 00/29] staging: bcm2835-audio: Cleanups and fixes Stefan Wahren
2018-09-08 16:21   ` Takashi Iwai
2018-09-08 17:00     ` Stefan Wahren
2018-09-08 17:16       ` Takashi Iwai
2018-09-10  9:12     ` Greg Kroah-Hartman
2018-09-10  9:16       ` Takashi Iwai

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