Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754764AbaKRSAv (ORCPT ); Tue, 18 Nov 2014 13:00:51 -0500 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:54071 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753627AbaKRSAt (ORCPT ); Tue, 18 Nov 2014 13:00:49 -0500 Date: Tue, 18 Nov 2014 18:00:37 +0000 From: Russell King - ARM Linux To: Andrew Jackson Cc: Dave Airlie , "dri-devel@lists.freedesktop.org" , "linux-kernel@vger.kernel.org" , Liviu Dudau , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] drm/i2c: tda998x: Allow for different audio sample rates Message-ID: <20141118180036.GC4042@n2100.arm.linux.org.uk> References: <546B8452.6030701@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <546B8452.6030701@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 18, 2014 at 05:39:30PM +0000, Andrew Jackson wrote: > On HDMI, the audio data are carried across the HDMI link which is > driven by the TDMS clock. The TDMS clock is dependent on the video pixel > rate. > > This patch sets the denominator (Cycle Time Stamp) appropriately > allowing the driver to send audio to a wider range of HDMI sinks > (i.e. monitors). This is actually pointless, because we don't use "manual" CTS mode. If the clocks for the video and audio are coherent, then you can program both the N and CTS values to allow the sink to properly recover the synchronous audio clock. However, in most cases, the audio and video clocks are not coherent, and since the recovered audio clock has to match the source audio clock, the only way this can be done is by the TDA998x (or in fact other HDMI encoder) to measure the audio clock rate and generate the CTS value itself. This is the mode we drive the TDA998x - so the programmed CTS value is irrelevant. See the HDMI spec, section 7.2 for a discussion about this, especially non-coherent clocks. -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/