From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: [PATCH] ASoC: omap-mcbsp: Add PM QoS support for McBSP to prevent glitches Date: Fri, 2 Sep 2016 17:54:37 +0200 Message-ID: <20160902155437.GA4152@amd> References: <20160829182746.53vrgbxadqodzzug@atomide.com> <925ded57-1e91-3db6-9e82-3a3ff5775412@ti.com> <20160831141340.h24szdqjnicmt2ew@atomide.com> <20160831165959.3sldcjxaci3kdx6z@atomide.com> <20160831194107.wijnbmdns2jjvzkv@atomide.com> <5af44090-6902-2ade-be78-378843757a0a@ti.com> <20160901145006.xr3ux63cg6f5bh7p@atomide.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Peter Ujfalusi Cc: alsa-devel@alsa-project.org, Ivaylo Dimitrov , Aaro Koskinen , Tony Lindgren , Liam Girdwood , Sebastian Reichel , "Kristo, Tero" , Mark Brown , Jarkko Nikula , Pali =?iso-8859-1?Q?Roh=E1r?= , linux-omap@vger.kernel.org List-Id: linux-omap@vger.kernel.org Hi! > >> When the FIFO is set to 128, it means that after the initial FIFO fill we will > >> have DMA request coming from McBSP to sDMA with a rate of: > >> > >> (1000/sampling_rate) * (FIFO-threshold / channels) = DMA_req_distance_in_ms > >> > >> So in case of 44.1KHz, stereo with 128 FIFO threshold DMA request will come at > >> every 1.45ms. If I'm not mistaken. The whole FIFO (1280) holds 14.51ms of > >> audio in this case. > >> > >> I don't see this correlate with the 30ms at all. > > > > It seems we easily have a situation where DMA is done buffering to McBSP, > > and PMIC is playing audio, and we hit idle. At that point there are no immediate > > timers pending and cpuidle determines we can try to hit a deeper idle mode. As > > there are no hardware blockers with DMA off and McBSP not blocking, the hardware > > hits off mode. This cuts power to McBSP. > > > > Ideally we'd configure McBSP activity to block deeper idle states in the > > hardware but I don't think we have such a configuration available. > > I wonder why we have not seen this before? I can not recall anything like this > with n900 (Jarkko might know that better) neither with n9/n950. On the n9/n950 > I have even put the OMAP3 to OFF during audio playback with the I was seeing something like that with 4.x kernel on Nokia N900. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html