Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935000AbdCJK6z (ORCPT ); Fri, 10 Mar 2017 05:58:55 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:38507 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934888AbdCJK6Y (ORCPT ); Fri, 10 Mar 2017 05:58:24 -0500 Subject: Re: [PATCH] drm: dw_hdmi: Gate audio sampler clock from the enablement functions To: Russell King - ARM Linux References: <20170310093509.19044-1-romain.perier@collabora.com> <20170310094613.GQ21222@n2100.armlinux.org.uk> <7888eb1f-2781-d4ed-6f26-cb76e1ead4d2@collabora.com> <20170310102753.GR21222@n2100.armlinux.org.uk> Cc: Archit Taneja , David Airlie , Heiko Stuebner , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org From: Romain Perier Message-ID: <202cd871-eb1c-d8f4-62d6-bed479f0eece@collabora.com> Date: Fri, 10 Mar 2017 11:58:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20170310102753.GR21222@n2100.armlinux.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2550 Lines: 57 Hello, Le 10/03/2017 ? 11:27, Russell King - ARM Linux a ?crit : > On Fri, Mar 10, 2017 at 11:21:53AM +0100, Romain Perier wrote: >> Hello, >> >> Le 10/03/2017 ? 10:46, Russell King - ARM Linux a ?crit : >>> On Fri, Mar 10, 2017 at 10:35:09AM +0100, 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(). >>> How does this interact with the workaround given in my commit introducing >>> these functions? (Commit b90120a96608). >>> >>> Setting N=0 is a work-around for iMX6, and we need the audio FIFO to be >>> loaded with data prior to setting N non-zero. If disabling the audio >>> clock prevents the audio FIFO being loaded, your patch will break iMX6. >>> >> Mhhh, the fact is I have no IMX6 devices here (only Rockchip). So >> I only tested on Rockchip devices. An approach might be to introduce an >> option for handling this errata, because that's platform specific and >> other platforms (like Rockchip) are in conflict with this. > or are you saying > that the I2S driver was never functionally tested as working? No ^^ > > I also would not think that it's platform specific - remember that > this is Designware IP, and it's likely that other platforms with > exactly the same IP would suffer from the same problem. It's > probably revision specific, but we need Synopsis' input on that. > > However, I do believe that your patch probably doesn't have much > merit in any case: on a mode set, you enable the audio clock, and > it will remain enabled until the audio device is first opened and > then closed. If another mode set comes along, then exactly the > same situation happens again. So, really it isn't achieving all > that much. > The fact is we still have sound glitches caused by this workaround on Rockchip, we probably have a revision of the IP without this issue. If CTS+N is not forced to zero we no longer have the glitches :/ (with or without touching the clock) Romain