Re: [PATCH 7/7] ALSA: usb: take startup delay into account

[Takashi Iwai <tiwai@suse.de>]

On Mon, 03 Oct 2016 17:04:23 +0200,
Pierre-Louis Bossart wrote:
> 
> 
> >> For playback usages, the endpoints are started before the prepare
> >> step, and valid audio data will be rendered with a delay that
> >> cannot be recovered.
> >> Worst-case the initial delay due to buffering of empty URBS can
> >> be up to 12ms
> 
> > This is really a fix unlike other patches in the series.
> > Please split it from others, so that we can apply it easily.
> 
> There was also additional discussions on this topic since I put this
> together, not sure it makes sense to merge this patch at the moment.
> In the Windows driver, the URBs can be submitted at a specific time,
> which allows for synchronous starts of all endpoints (limited to the
> 1ms frame resolution). In Linux we can't since the start time is owned
> by the xhci driver and can't be modified by the class driver. I talked
> with Mathias Nyman and Baolu Lu on this before the summer and of
> course I became busy with other things. The short story is that there
> is a wider problem with USB start and linking endpoints that should be
> addressed as a single step. Maybe something to talk about at the
> miniconference?

Sure, why not.  Now it's close to LPC and we won't reach to the
solution soonish yet.


Takashi