From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfgang Grandegger Date: Fri, 18 May 2007 17:20:48 +0200 Subject: [U-Boot-Users] Ideas on U-Boot configuration with FDT In-Reply-To: <464DBFC8.4050708@freescale.com> References: <464D6D4A.4000200@grandegger.com> <464DB7C1.4050509@freescale.com> <464DBBB2.1060006@grandegger.com> <464DBCB4.3050409@freescale.com> <464DBFDD.6030209@grandegger.com> <464DBFC8.4050708@freescale.com> Message-ID: <464DC450.8040205@grandegger.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Timur Tabi wrote: > Wolfgang Grandegger wrote: > >> RAM is _not_ available at that stage. > > Do we really need RAM to parse the device tree and configure U-Boot? I > think not. But you need it anyhow in RAM for booting Linux. Why not doing it early, e.g. after relocation when memory is available. > The device tree has a memory section: > > memory { > device_type = "memory"; > reg = <00000000 10000000>; // 256MB > }; > > So the question is: do we want U-Boot to use this node to determine how > much RAM there is, or do we want U-Boot to determine how much RAM there > is and update this node? Both makes sense, I think. How we finally use FDT it U-Boot is not yet clear, but exhaustive usage like in the kernel seems not attractive to me. Currently I just need it do enable some devices dynamically, like PCMCIA, RTC and CAN and configure the LCD controller for various panels. >> Depends, you might be right for FLASH on a 32-bit bus. On slow ROM >> devices and slow processors, it matters. > > I still don't see how it's important. If the device tree is on slow > memory, so what? You have to read it sooner or later. If your board > can't handle this feature, then don't enable it, and configure U-Boot > the "old fashioned way". Don't like the "don't care" argument. If you can make your code faster, just do it. Wolfgang.