Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753748AbbHGOOB (ORCPT ); Fri, 7 Aug 2015 10:14:01 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:42341 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753323AbbHGON7 (ORCPT ); Fri, 7 Aug 2015 10:13:59 -0400 Date: Fri, 7 Aug 2015 15:13:46 +0100 From: Russell King - ARM Linux To: Sascha Hauer Cc: Thierry Reding , Philipp Zabel , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] drm: bridge/dw_hdmi: Cache edid data Message-ID: <20150807141346.GH7557@n2100.arm.linux.org.uk> References: <1438955961-27232-1-git-send-email-s.hauer@pengutronix.de> <1438955961-27232-2-git-send-email-s.hauer@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438955961-27232-2-git-send-email-s.hauer@pengutronix.de> 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 Content-Length: 1470 Lines: 29 On Fri, Aug 07, 2015 at 03:59:20PM +0200, Sascha Hauer wrote: > Instead of rereading the edid data each time userspace asks for them > read them once and cache them in the previously unused edid field in > struct dw_hdmi. This makes the code a little bit more efficient. How has this been tested? Has it been tested with an AV amplifier in the path to the display device? If not, it really needs to be tested, because such devices modify the EDID data, or subsitute their own, and alter the EDID data depending on their needs. When they do, they lower and re-assert the HPD signal, possibly for as little as 100ms - defined by the HDMI spec. For example, an AV amplifier in standby can provide the displays EDID in the first page of EDID, along with the displays extended EDID in the second page. When the AV amplifier is powered up, it can provide a different second page of EDID information detailing the audio formats that it can accept, and it will lower and re-assert the HPD signal to cause the connected devices to read the updated EDID information. Same thing can happen when switching to standby mode too. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps 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/