From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Antonino A. Daplas" Subject: Re: Driver for Sharp LH155BA Date: Tue, 01 Aug 2006 08:35:57 +0800 Message-ID: <44CEA1ED.8030103@gmail.com> References: <170385E48B041543AC99CCD09E325AD1952BB0@mail.rogermanagement.com.au> Reply-To: linux-fbdev-devel@lists.sourceforge.net Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from sc8-sf-mx2-b.sourceforge.net ([10.3.1.92] helo=mail.sourceforge.net) by sc8-sf-list1-new.sourceforge.net with esmtp (Exim 4.43) id 1G7iEz-00089t-KH for linux-fbdev-devel@lists.sourceforge.net; Mon, 31 Jul 2006 17:36:09 -0700 Received: from ug-out-1314.google.com ([66.249.92.171]) by mail.sourceforge.net with esmtp (Exim 4.44) id 1G7iEy-00057o-7T for linux-fbdev-devel@lists.sourceforge.net; Mon, 31 Jul 2006 17:36:09 -0700 Received: by ug-out-1314.google.com with SMTP id s2so1026008uge for ; Mon, 31 Jul 2006 17:36:04 -0700 (PDT) In-Reply-To: <170385E48B041543AC99CCD09E325AD1952BB0@mail.rogermanagement.com.au> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-fbdev-devel-bounces@lists.sourceforge.net Errors-To: linux-fbdev-devel-bounces@lists.sourceforge.net To: linux-fbdev-devel@lists.sourceforge.net Richard Wolf wrote: > Hi, > > I'm writing a driver for the Sharp LH155BA LCD driver. This is a driver > designed for controlling small/medium lcd panels (up to 128 x 64 pixels). > > I'm trying to decide whether it is sensible to write a frame buffer driver > for a device of this nature. Does the frame buffer abstraction make sense > for a display this small? The dimensions of the display does not matter. > > On our target hardware it is not possible to access the display memory > directly. Rather, all accesses to display memory and other control > registers are through a small number of io ports. Therefore it is not > possible to map display memory. Is this relevant? Yes, if the display memory is not mappable, then it won't be usable as a driver for X, for example. You can however allocate a shadow buffer in system RAM which can be mmapp'ed. Then on intervals, perhaps by interrupt or timer, update the physical screen. Unfortunately, this is inefficient, as you may be updating the screen even if the shadow buffer haven't changed. But that is the best you can do without hacking the kernel. Another option is to just forget about mmap, and create your own fb_read and fb_write hooks. This is more efficient, but not all apps use this method to update the framebuffer. The driver will be usable as a console though. Tony ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV