From e69f202d0a1419219198566e1c22218a5c71a9a6 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Thu, 7 Dec 2006 02:14:04 +0100 Subject: [PATCH] i386: Implement CONFIG_PHYSICAL_ALIGN o Now CONFIG_PHYSICAL_START is being replaced with CONFIG_PHYSICAL_ALIGN. Hardcoding the kernel physical start value creates a problem in relocatable kernel context due to boot loader limitations. For ex, if somebody compiles a relocatable kernel to be run from address 4MB, but this kernel will run from location 1MB as grub loads the kernel at physical address 1MB. Kernel thinks that I am a relocatable kernel and I should run from the address I have been loaded at. So somebody wanting to run kernel from 4MB alignment location (for improved performance regions) can't do that. o Hence, Eric proposed that probably CONFIG_PHYSICAL_ALIGN will make more sense in relocatable kernel context. At run time kernel will move itself to a physical addr location which meets user specified alignment restrictions. Signed-off-by: Vivek Goyal Signed-off-by: Andi Kleen --- arch/i386/Kconfig | 33 ++++++++++++++++++--------------- 1 file changed, 18 insertions(+), 15 deletions(-) (limited to 'arch/i386/Kconfig') diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig index d588ca874bb..fd2fa7a7ec5 100644 --- a/arch/i386/Kconfig +++ b/arch/i386/Kconfig @@ -785,23 +785,26 @@ config RELOCATABLE must live at a different physical address than the primary kernel. -config PHYSICAL_START - hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP) - - default "0x1000000" if CRASH_DUMP +config PHYSICAL_ALIGN + hex "Alignment value to which kernel should be aligned" default "0x100000" + range 0x2000 0x400000 help - This gives the physical address where the kernel is loaded. Normally - for regular kernels this value is 0x100000 (1MB). But in the case - of kexec on panic the fail safe kernel needs to run at a different - address than the panic-ed kernel. This option is used to set the load - address for kernels used to capture crash dump on being kexec'ed - after panic. The default value for crash dump kernels is - 0x1000000 (16MB). This can also be set based on the "X" value as - specified in the "crashkernel=YM@XM" command line boot parameter - passed to the panic-ed kernel. Typically this parameter is set as - crashkernel=64M@16M. Please take a look at - Documentation/kdump/kdump.txt for more details about crash dumps. + This value puts the alignment restrictions on physical address + where kernel is loaded and run from. Kernel is compiled for an + address which meets above alignment restriction. + + If bootloader loads the kernel at a non-aligned address and + CONFIG_RELOCATABLE is set, kernel will move itself to nearest + address aligned to above value and run from there. + + If bootloader loads the kernel at a non-aligned address and + CONFIG_RELOCATABLE is not set, kernel will ignore the run time + load address and decompress itself to the address it has been + compiled for and run from there. The address for which kernel is + compiled already meets above alignment restrictions. Hence the + end result is that kernel runs from a physical address meeting + above alignment restrictions. Don't change this unless you know what you are doing. -- cgit v1.2.3