From mboxrd@z Thu Jan 1 00:00:00 1970 From: Clemens Ladisch Subject: Re: Multiple channels mapping Date: Wed, 08 Feb 2012 12:32:17 +0100 Message-ID: <4F325D41.50304@ladisch.de> References: <4F31C988.3090201@codeaurora.org> <4F323DE5.4050108@ladisch.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from out5-smtp.messagingengine.com (out5-smtp.messagingengine.com [66.111.4.29]) by alsa0.perex.cz (Postfix) with ESMTP id D8354103DFA for ; Wed, 8 Feb 2012 12:30:11 +0100 (CET) Received: from compute2.internal (compute2.nyi.mail.srv.osa [10.202.2.42]) by gateway1.nyi.mail.srv.osa (Postfix) with ESMTP id 0B20520B46 for ; Wed, 8 Feb 2012 06:30:09 -0500 (EST) In-Reply-To: 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: Takashi Iwai Cc: alsa-devel List-Id: alsa-devel@alsa-project.org Takashi Iwai wrote: > Clemens Ladisch wrote: >> Takashi Iwai wrote: >>> Currently the channel-mapping information is a missing piece in ALSA >>> framework, and it's a very long-standing item on my TODO list. >>> >>> The implementation itself should be easy, but the only question is the >>> API design. If you have a good proposal, please speak up. >> >> TLVs on media controller entities. > > Well, my concern is that it might be too far from the other PCM > stuff. How the implementation would look like? There is one media controller device node per device (= ALSA card), containing multiple entities (similar to how a ctl device contains multiple controls). /dev/media42 _is_ separate, but the entity that represents a PCM device is handled by the PCM code, so it would be possible to have a shortcut to get a PCM device's TLVs directly. > More question is whether this information should be available before > or after hw_params setup. This is pretty much static information, which is available even when the PCM device isn't opened. > BTW, the channel-mapping info can be useful for the automatic plug > layer, too. And if there is a need for channel mapping information of ALSA plugins, there needs to be a userspace library for the media controller API. Regards, Clemens