Messages in this thread | | | Subject | Re: [PATCH 17/29] staging: bcm2835-audio: Add 10ms period constraint | From | Mike Brady <> | Date | Wed, 19 Sep 2018 13:47:46 +0100 |
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Hi Stefan. Thanks for this.
> On 19 Sep 2018, at 13:41, Stefan Wahren <stefan.wahren@i2se.com> wrote: > > Hi, > > [add Phil and Mike] > > Am 19.09.2018 um 11:52 schrieb Takashi Iwai: >> 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. > > thanks for your explanation. So your patch must be reverted with > implementation of interpolate audio delay. > >> >>> [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. > > I think we should try to implement this later. > > @Mike: Do you want to write a patch series which upstream "interpolate > audio delay" and addresses Takashi's comments? > > I would help you, in case you have questions about setup a Raspberry Pi > with Mainline kernel or patch submission.
Yeah, sure. I might need some of the handholding alright. Can you point me at any documentation please? Regards Mike
> > Regards > Stefan > >> >> >> thanks, >> >> Takashi > >
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