From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935106AbaKNEIc (ORCPT ); Thu, 13 Nov 2014 23:08:32 -0500 Received: from smtp.codeaurora.org ([198.145.11.231]:41874 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933512AbaKNEI3 (ORCPT ); Thu, 13 Nov 2014 23:08:29 -0500 Message-ID: In-Reply-To: <5464CDE2.2070406@linux.intel.com> References: <85499f52ebd29581bf58b9cafbae6864.squirrel@www.codeaurora.org> <5464CDE2.2070406@linux.intel.com> Date: Fri, 14 Nov 2014 04:08:28 -0000 Subject: Re: [alsa-devel] Question on Compressed offload session From: gsantosh@codeaurora.org To: "Pierre-Louis Bossart" Cc: gsantosh@codeaurora.org, alsa-devel-bounces@alsa-project.org, "Mark Rutland" , "Rob Herring" , "ALSA Development Mailing List" , "Kuninori Morimoto" , "Stephen Warren" , "Linux-sh list" , "Magnus" , linux-kernel@vger.kernel.org, grant.likely@linaro.org, devicetree@vger.kernel.org, "Mark Brown" , "Geert Uytterhoeven" , "Olof Johansson" , "Kuninori Morimoto" User-Agent: SquirrelMail/1.4.22-4.el6 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On 11/12/14, 9:02 PM, gsantosh@codeaurora.org wrote: >> Hi All, >> >> The Question is for the compressed offload session. >> >> For a generic codec driver during the startup function it will set some >> of >> the hw_constraints rule similarly like this. >> >> snd_pcm_hw_constraint_list(substream->runtime, 0, >> SNDRV_PCM_HW_PARAM_RATE, >> &constraints_12_24); >> >> pcm_lib.c will try to add the rule to the runtime structure by accessing >> the pointers which will be initialized during opening of the session, >> as The Constraints added by the codec driver will be updated in the >> >> struct snd_pcm_hw_constraints of runtime structure which will be part of >> substream handle. >> >> But for the compressed offload I do not see the initialization done for >> HW >> constraints, as done in pcm session >> >> 2092int snd_pcm_open_substream(struct snd_pcm *pcm, int stream, >> 2093 struct file *file, >> 2094 struct snd_pcm_substream **rsubstream) >> >> most of the existing drivers which has the hw_constraint_list code will >> not be applicable for compress offload session, how to solve this? > > You can't directly link physical output/input with the decoder/encoder > in general. > For decoders, the sample-rate may not always be known ahead of time, > e.g. with AAC-SBR implicit signaling. There is no way to add constraints > on open, there is an assumption that a sample-rate converter is part of > the chain to take care of the difference between the output of the > offloaded decoder and the back-end actual sampling frequency (same with > number of channels and bit-width btw). > Likewise if you encode the frequency may not be the same as what the > backend provides and some SRC might be needed. > -Pierre > I Agree we cannot have a direct link between physical output / input with decoder / encoder, during compressed playback. My concern here is, if we have a legacy codec driver which is used for the PCM out, and in the start up of this codec driver it is adding hw_constraints list, now the same codec driver is used for the compressed session FE or PCM session FE, If the routing is such that compressed FE -> codec the hw_constraints added by this driver is not valid here, and legacy drivers needs to be changed, Now the question comes how to change this drivers? I can think of following things if the routing is done for Compressed FE -> codec 1) in Codec driver avoid adding hw_constraint during startup if compressed session is routed, this recommend for codec driver to know that compress session is routed to codec which I feel not the correct way to handle this I was checking how to handle this situation in much better way. Regards Santosh > _______________________________________________ > Alsa-devel mailing list > Alsa-devel@alsa-project.org > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel >