On Thu, Apr 08, 2010 at 10:53:25AM +0100, Mark Brown wrote: > On Thu, Apr 08, 2010 at 11:31:26AM +0200, Sascha Hauer wrote: > > > - /* Restart the timer; if we didn't report we'll run on the next tick */ > > - add_timer(&iprtd->timer); > > + hrtimer_forward_now(hrt, ns_to_ktime(iprtd->poll_time_ns)); > > Hrm, this looks like it's going to have an issue with clock drift - > we're now unconditionally advancing the timer every period, even if the > data transfer hasn't pushed through a period of data. This will cause > problems on lengthy playbacks (and shorter ones if the clocks are > sufficiently out of sync). We are calling snd_pcm_period_elapsed when at least one period is over. As I see it the worst thing that could happen is that we have not transfered enough data for one period in the timer callback and thus we call snd_pcm_period_elapsed in the next timer callback, so about one period too late, but the comment in sound/core/pcm_lib.c says: Even if more than one periods have elapsed since the last call, you have to call this only once. So I think this should be save. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
