Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753268AbdCMM4i (ORCPT ); Mon, 13 Mar 2017 08:56:38 -0400 Received: from us01smtprelay-2.synopsys.com ([198.182.47.9]:58954 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753217AbdCMM4N (ORCPT ); Mon, 13 Mar 2017 08:56:13 -0400 Subject: Re: [PATCH] drm: dw_hdmi: Gate audio sampler clock from the enablement functions To: Russell King - ARM Linux , Neil Armstrong References: <20170310093509.19044-1-romain.perier@collabora.com> <25ad96a7-d907-2bcb-3a96-15a2956e7652@baylibre.com> <20170313093630.GE21222@n2100.armlinux.org.uk> CC: Romain Perier , Jose Abreu , Archit Taneja , "David Airlie" , Heiko Stuebner , , , , From: Jose Abreu Message-ID: <724d599e-7285-3feb-9a18-d3fbc4000eb5@synopsys.com> Date: Mon, 13 Mar 2017 12:55:58 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20170313093630.GE21222@n2100.armlinux.org.uk> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.107.19.121] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2313 Lines: 56 Hi, On 13-03-2017 09:36, Russell King - ARM Linux wrote: > On Mon, Mar 13, 2017 at 10:27:08AM +0100, Neil Armstrong wrote: >> On 03/10/2017 10:35 AM, Romain Perier wrote: >>> Currently, the audio sampler clock is enabled from dw_hdmi_setup() at >>> step E. and is kept enabled for later use. This clock should be enabled >>> and disabled along with the actual audio stream and not always on (that >>> is bad for PM). Futhermore, this might cause sound glitches with some >>> HDMI devices, as the CTS+N is forced to zero when the stream is disabled >>> while the audio clock is still running. >>> >>> This commit adds a parameter to hdmi_audio_enable_clk() that controls >>> when the audio sample clock must be enabled or disabled. Then, it moves >>> the call to this function into dw_hdmi_audio_enable() and >>> dw_hdmi_audio_disable(). >>> >>> Signed-off-by: Romain Perier >>> --- >>> drivers/gpu/drm/bridge/dw-hdmi.c | 15 +++++++++------ >>> 1 file changed, 9 insertions(+), 6 deletions(-) >>> >> Hi Romain, Russell, Jose, >> >> This is a little out of scope, but I was wondering why the CTS calculation >> was not left in AUTO mode in the dw-hdmi driver ? > There is no indication in the iMX6 manuals that the iMX6 supports > automatic CTS calculation. Bits 7:4 of the AUD_CTS3 register are > marked as "reserved". > > We're reliant on the information in the iMX6 manuals as we don't have > access to Synopsis' databooks for these parts (I understand you have > to be a customer to have access to that.) > (Synopsis -> Synopsys :)) Trying to catch up with the conversation: 1) In AHB audio mode the bits are always reserved. 2) I think we should enable/disable clock instead of just forcing N/CTS, though, I don't know what could be the implications for iMX platform. I remember at the time I tested this using I2S (I've never used AHB), and HDMI protocol analyzers were complaining about the N/CTS being forced to zero. 3) I also remember that there was something wrong with the N calculations (I had to remove the if for pixel clock == 25175000). I never submited a patch to that because I was running out of time and didn't investigate this further (it could be for example a problem specific to my setup). Hope it helps a little bit. Best regards, Jose Miguel Abreu