From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anssi Hannula Subject: Re: [PATCH RFC v2 10/13] sound/core: add DRM ELD helper Date: Wed, 06 May 2015 20:02:52 +0300 Message-ID: <554A493C.5080106@iki.fi> References: <20150402092050.GH24899@n2100.arm.linux.org.uk> <20150405162034.GH13898@n2100.arm.linux.org.uk> <20150405172608.GA12732@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail3.ippnet.fi (mail3.ippnet.fi [62.197.168.3]) by alsa0.perex.cz (Postfix) with ESMTP id 47739260713 for ; Wed, 6 May 2015 19:03:01 +0200 (CEST) In-Reply-To: <20150405172608.GA12732@n2100.arm.linux.org.uk> 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: Russell King - ARM Linux Cc: Fabio Estevam , alsa-devel@alsa-project.org, Takashi Iwai , dri-devel@lists.freedesktop.org, Mark Brown , Yakir Yang , linux-arm-kernel@lists.infradead.org List-Id: alsa-devel@alsa-project.org 05.04.2015, 20:26, Russell King - ARM Linux kirjoitti: > On Sun, Apr 05, 2015 at 06:46:13PM +0200, Takashi Iwai wrote: >> >> One another question: don't we need to deal with the sample bits in >> sad[2]? > > It should, but I'm very wary about doing that without seeing more > examples of real SADs. Right now, all my examples only support > one SAD with either 2 channel or 6 channel audio at the standard > (basic) 32, 44.1 and 48kHz rates. > > The HDMI / CEA specs are very loose in their wording about the > short audio descriptors. I've no idea whether a sink can provide > (for example) descriptors such as: > > LPCM, 6 channel 32, 44.1, 48kHz > LPCM, 2 channel, 32, 44.1, 48, 96, 192kHz > > or whether have to describe that as a single descriptor. I only > have two TVs to test with here. For the record, yes, multiple LPCM SADs are relatively common, and I think I've seen some that offered more rates on a stereo SAD than on a multichannel SAD (like in your example). > What I'm concerned about is that when the ALSA parameter refining > starts, we start with (eg) 2-8 channels, 32-192kHz. Given that, > if we invoke the channel restriction before the rate restriction, > we would end up limiting to 2 channel at 32-192kHz. If we apply > the restrictions in the opposite order, we'd restrict to 6 > channel, 32-48kHz. Neither are obviously correct in this > circumstance, and I don't really see a way to solve it given my > understanding of the way ALSA's parameter refinement works. > > I suspect this is why most HDMI drivers are implemented such that > they take the maximum capabilities over all SADs, which would end > up restricting audio in the above case to: up to 6 channels, at > 32, 44.1, 48, 96 and 192kHz, even though 6 channel @ 192kHz isn't > hasn't been indicated as supported. > > Most of this is speculation though, based off what is in the > documentation. As I say, I don't have enough real-world examples > to get a feel for what manufacturers _actually_ do to give a hint > as to how the documentation should be interpreted. > > So, maybe I should just copy what everyone else does and take the > maximum of all descriptors... > -- Anssi Hannula