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Date: Sun, 20 Apr 2008 21:54:13 -0700 From: "Yinghai Lu" <yhlu.kernel@...il.com> To: "Mitch Bradley" <wmb@...mworks.com> Cc: "H. Peter Anvin" <hpa@...or.com>, "Andres Salomon" <dilinger@...ued.net>, "Eric W. Biederman" <ebiederm@...ssion.com>, "Ingo Molnar" <mingo@...e.hu>, "Andrew Morton" <akpm@...ux-foundation.org>, "Joseph Fannin" <jfannin@...il.com>, linux-kernel@...r.kernel.org, jordan.crouse@....com Subject: Re: [PATCH 1/2] OLPC: Add support for calling into Open Firmware On Sun, Apr 20, 2008 at 8:39 PM, Mitch Bradley <wmb@...mworks.com> wrote: > > H. Peter Anvin wrote: > > > Mitch Bradley wrote: > > > > > > > > The x86 architecture doesn't make this problem easy. > > > > > > > > > > [long rant about the x86 architecture] > > > > It would be more useful if you described the actual defined entry > conditions from OpenFirmware look like, including if they are well-defined > for all OF implementations or only for OLPC. > > > > -hpa > > > > Fair enough... > > To get the second subquestion out of the way: At the present time, on the > x86 architecture, "all OF implementations" and "OLPC" are effectively the > same. I am unaware of any other x86 OFW deployments in current use. There > have been some in the past, on bespoke systems such as Network Appliance > servers and at least one settop box, but those have fallen by the wayside as > those companies have shifted over to commodity PC hardware. The current > market status quo is that x86 boards are primarily designed for Windows, and > thus must run legacy BIOS, with some recent migration to EFI, neither of > which are open source in the strong sense. While I would like to see more > OFW penetration into the larger x86 market, I don't really expect it. x86 > motherboard manufacturing is becoming more and more difficult as signal > speeds increase, leading to a decline in the number of manufacturers. The > existing manufacturers depend on Windows for sales volume and their internal > procedures and working knowledge are based on legacy BIOS. > > Once upon a time, we had an OFW "binding" document that stipulated the > interface conditions, with the intention of making that "standard" across > all OFW-on-x86 systems. However, by the time OLPC came around, there were > no other systems to consider, so I felt free to make some changes in the > interface. I ended up choosing an ABI that resulted in a simple (in the > sense of not much code, and no complex state transitions) interface with 2.6 > Linux kernels. > > The interface defined below is not inherently OLPC-specific - it would be > suitable for any ia32 system that used OFW. (At a higher level, the set of > OFW callback functions is architecture-neutral; in this message I am > focusing on the very low-level details of the ia32 ABI) > > The system conditions for the OFW to Linux kernel transition are as > follows: > > a) OFW can load the Linux kernel from either bzimage format or ELF format > (either uncompressed or zlib-compressed.) If the kernel is in ELF format > with symbols, OFW can do symbolic kernel debugging. Further discussion will > focus on bzimage format, as that is what OLPC uses and is also the "greased > path" for kernel builds. > > b) OFW loads the bzimage kernel at 0x100000 and the ramdisk image, if any, > at 0x800000. so you are assuming that your uncompressed vmlinux only use less 8M space? you are supposed to check the bzImage to get uncompressed vmlinux size. YH -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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