From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kronos Subject: Re: [PATCH] radeonfb: DDC i2c fix Date: Sat, 12 Mar 2005 02:06:13 +0100 Message-ID: <20050312010613.GA14837@dreamland.darkstar.lan> References: <1110519970.5751.17.camel@gaston> <20050311201326.GA7379@dreamland.darkstar.lan> <1110585137.5751.122.camel@gaston> Reply-To: linux-fbdev-devel@lists.sourceforge.net Mime-Version: 1.0 Received: from sc8-sf-mx1-b.sourceforge.net ([10.3.1.11] helo=sc8-sf-mx1.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Exim 4.30) id 1D9v4W-00038M-Oe for linux-fbdev-devel@lists.sourceforge.net; Fri, 11 Mar 2005 17:05:40 -0800 Received: from mail-relay-4.tiscali.it ([213.205.33.44]) by sc8-sf-mx1.sourceforge.net with esmtp (Exim 4.41) id 1D9v4V-0002eC-2o for linux-fbdev-devel@lists.sourceforge.net; Fri, 11 Mar 2005 17:05:40 -0800 Content-Disposition: inline In-Reply-To: <1110585137.5751.122.camel@gaston> Sender: linux-fbdev-devel-admin@lists.sourceforge.net Errors-To: linux-fbdev-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: List-Post: List-Help: List-Subscribe: , List-Archive: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Benjamin Herrenschmidt Cc: Kronos , Linux Fbdev development list , Andrew Morton Il Sat, Mar 12, 2005 at 10:52:17AM +1100, Benjamin Herrenschmidt ha scritto: > On Fri, 2005-03-11 at 21:13 +0100, Kronos wrote: > > Il Fri, Mar 11, 2005 at 04:46:10PM +1100, Benjamin Herrenschmidt ha scritto: > > > The radeonfb code for DDC probing (like it's X.org counterpart) uses to > > > leave the DDC clock & data lines asserted after the probing is complete. > > > This causes problems with some Apple monitors like the new Cinema HD > > > 23", who will turn themselves off when that happens. This fixes it. > > > > Fix is correct, but comment is not ;) After the loop SCL and SDA are > > left low. Pulling them high puts the I2C bus in the stop condition. > > Well, they are pull-up lines. I'm not pulling them high per-se, I'm > "releasing" them to their natural state, which is high ;) The ATI code > does some weird shit around the i2c transfer proper, and I don't know > exactly why. When I wrote that code I asked a clarification from ATI (IIRC I spoke with Hui Yu) and they said that it was needed to cover some strange corner case. My tests showed that I was able to read EDID even without that black magic but since the code originated from ATI I left it in place. > I don't have any spec about DDC2 though, my understand is > that it's more than just i2c EEPROM though. I don't have DDC2 spec because VESA.org prices are too high... but I know that it's based on I2C protocol and it follows I2C format (ie. start-stop sequencies and so on). AFAIK for EDID initiating a read at the right address is enough, but DDC2 is meant to be bi-directional to control brightness, contrast, you name it. I'm clueless on this part of DCC2. Luca -- Home: http://kronoz.cjb.net Il piu` bel momento dell'amore e` quando ci si illude che duri per sempre; il piu` brutto, quando ci si accorge che dura da troppo. ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click