From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sascha Hauer Subject: Re: [PATCH 3/3] imx-ssi: Use a hrtimer in FIQ mode Date: Thu, 8 Apr 2010 15:13:53 +0200 Message-ID: <20100408131353.GI3688@pengutronix.de> References: <1270719086-23453-1-git-send-email-s.hauer@pengutronix.de> <1270719086-23453-4-git-send-email-s.hauer@pengutronix.de> <20100408095324.GB6303@rakim.wolfsonmicro.main> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [92.198.50.35]) by alsa0.perex.cz (Postfix) with ESMTP id ECB1E243DC for ; Thu, 8 Apr 2010 15:13:53 +0200 (CEST) Content-Disposition: inline In-Reply-To: <20100408095324.GB6303@rakim.wolfsonmicro.main> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Mark Brown Cc: alsa-devel@alsa-project.org, Valentin Longchamp List-Id: alsa-devel@alsa-project.org 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 |