From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Ujfalusi Subject: Re: [PATCH 11/20] OMAP: McBSP: Add link DMA mode selection Date: Thu, 13 Aug 2009 09:01:24 +0300 Message-ID: <200908130901.25420.peter.ujfalusi@nokia.com> References: <1248958183-15015-1-git-send-email-eduardo.valentin@nokia.com> <20090812144547.eb4bf7f2.jhnikula@gmail.com> <1250077713.16045.31.camel@eenurkka-desktop> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mgw-mx03.nokia.com (smtp.nokia.com [192.100.122.230]) by alsa0.perex.cz (Postfix) with ESMTP id 35A0B248C0 for ; Thu, 13 Aug 2009 08:01:34 +0200 (CEST) In-Reply-To: <1250077713.16045.31.camel@eenurkka-desktop> Content-Disposition: inline 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: "Nurkkala Eero.An (EXT-Offcode/Oulu)" Cc: "alsa-devel@alsa-project.org" , "linux-omap@vger.kernel.org" , "alsa-devel@vger.kernel.org" List-Id: alsa-devel@alsa-project.org On Wednesday 12 August 2009 14:48:33 Nurkkala Eero.An (EXT-Offcode/Oulu) wr= ote: > On Wed, 2009-08-12 at 13:45 +0200, ext Jarkko Nikula wrote: > > The threshold based transfer will cause that omap_pcm_pointer will > > loose a bit its accuracy. Probably irrelevant but still better to play > > safe at least over one kernel release before making it default. > > No, it doesn't loose accuracy =3D) It's as accurate with both modes. > The difference is, that the other does things in bursts; In element mode it is kind of easy to estimate where the hardware actually = in = the playback case (aplay -f dat /dev/zero): omap_pcm_pointer returns 669, than the HW is around 669-512=3D157 (plus few samples). In threshold mode you only know that the HW is playing in between 0-512, = 512-1024 somewhere. I know neither of these are accurate and these examples are quite = oversimplified, but there is a difference and that difference is quite = significant. > that's called evolution rather than regression =3D) Note that evolution can also introduce regression... > That's how things will be in the future =3D) I agree with you on this, since the threshold mode provides quite good powe= r = saving benefits. But on the other hand it would be still better to keep the element mode as = default for at least one release cycle. If no report is coming about problems, than we can make the threshold mode = for = McBSP2 as the default -- = P=E9ter