From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Brown Subject: Re: [PATCH 1/2] ASoC: Allow drivers to specify how many bits are significant on a DAI Date: Tue, 17 Jan 2012 14:56:47 +0000 Message-ID: <20120117145646.GG2944@opensource.wolfsonmicro.com> References: <1326739267-9678-1-git-send-email-broonie@opensource.wolfsonmicro.com> <4F15377B.6080108@ti.com> <20120117113848.GE2944@opensource.wolfsonmicro.com> <4F157264.5020102@ti.com> <20120117131950.GF2944@opensource.wolfsonmicro.com> <4F15833B.2000808@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from opensource.wolfsonmicro.com (opensource.wolfsonmicro.com [80.75.67.52]) by alsa0.perex.cz (Postfix) with ESMTP id 1435B24425 for ; Tue, 17 Jan 2012 15:56:57 +0100 (CET) Content-Disposition: inline In-Reply-To: <4F15833B.2000808@ti.com> 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: Peter Ujfalusi Cc: alsa-devel@alsa-project.org, patches@opensource.wolfsonmicro.com, Liam Girdwood List-Id: alsa-devel@alsa-project.org On Tue, Jan 17, 2012 at 03:18:35PM +0100, Peter Ujfalusi wrote: > It is mostly true. DAC33 can be configured to operate internally 16bit > or 24msbit/32bit for example. Well, if it's doing something more complicated that doesn't fit in the framework then it shouldn't be doing that. > It does not give any useful information for application that the codec > will upsample the 16bit data internally to 24 bits. It does not really > matter for them since all 16bit data will be used by the codec. Oh, I dunno - I'm sure someone could think of a use for it. > > On the CPU side specifying significant bits would normally only be > > appropriate on PDM interfaces as they have most of a DAC or ADC in them > > to move between the sampled and PDM formats. I'd be surprised to see > > anything else setting these flags, most of the hardware is just passing > > the data straight through. > True, the CPU side mostly passes the data as it is, it does not care > about msbits. For McPDM it is different since the internal FIFO in 24bit > long word lines, so if application would use all 32bit we it will loose Right, like I say that's because it's got most of a DAC in it. > 8bit lsb. This can make difference for PA when applying the digital gain > in SW. Well, it saves it a bit of effort but that's about it.