Re: [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize

[Jiada Wang]

Hello Takashi

On 11/30/2016 05:54 PM, Takashi Iwai wrote:
> On Wed, 30 Nov 2016 08:59:21 +0100,
> Jiada Wang wrote:
> > From: Andreas Pape <apape@xxxxxxxxxxxxxx>
> >
> > since commit 57e6dae1087bbaa6b33d3dd8a8e90b63888939a3 the expected packetsize is always limited to
>
> Please use a form with 12 chars SHA ID plus the commit subject, e.g.
> 1234567890ab ("blah blah...")
I will update changelog as you have suggested in v2.
> > nominal + 25%. It was discovered, that some devices have a much higher jitter
> > in used packetsizes than 25% which would result in BABBLE condition and dropping of packets.
> > A better solution is so assume the jitter to be the nominal packetsize:
> > -one nearly empty packet followed by a almost double sized one.
>
> The increase of the max frequency is supposedly OK.
> A remaining question is whether this should be included in stable
> kernel.  It fixes in one side, but it's quite untested in another
> side.  Maybe we queue this for 4.10, and later on notify to stable
> maintainer once when it's confirmed to work and be harmless.
this makes sense to me

Thanks,
Jiada
> thanks,
>
> Takashi
>
> > Signed-off-by: Andreas Pape <apape@xxxxxxxxxxxxxx>
> > Signed-off-by: Jiada Wang <jiada_wang@xxxxxxxxxx>
> > ---
> >  sound/usb/endpoint.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
> > index c470251..2f592dd 100644
> > --- a/sound/usb/endpoint.c
> > +++ b/sound/usb/endpoint.c
> > @@ -632,8 +632,8 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
> >  	ep->stride = frame_bits >> 3;
> >  	ep->silence_value = pcm_format == SNDRV_PCM_FORMAT_U8 ? 0x80 : 0;
> >
> > -	/* assume max. frequency is 25% higher than nominal */
> > -	ep->freqmax = ep->freqn + (ep->freqn >> 2);
> > +	/* assume max. frequency is double than nominal */
> > +	ep->freqmax = ep->freqn * 2;
> >  	/* Round up freqmax to nearest integer in order to calculate maximum
> >  	 * packet size, which must represent a whole number of frames.
> >  	 * This is accomplished by adding 0x0.ffff before converting the
> > --
> > 2.9.3