Hi Simon, On Mon, Mar 7, 2016 at 10:28 AM, Simon Glass <s...@chromium.org> wrote: > Sometimes it is useful to jump into U-Boot directly from coreboot or UEFI > without any 16-bit init. This can help during development by allowing U-Boot > to avoid doing all the init required by the platform.
I don't understand, why is coreboot having a problem here? > > In this case we cannot rely on the GDT settings. U-Boot will hang or crash > if these are wrong. Provide a development-only option to set up the GDT > correctly. > > Signed-off-by: Simon Glass <s...@chromium.org> > --- > > arch/x86/cpu/start.S | 79 > ++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 79 insertions(+) > > diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S > index 485868f..5fbc2b5 100644 > --- a/arch/x86/cpu/start.S > +++ b/arch/x86/cpu/start.S > @@ -18,6 +18,13 @@ > #include <generated/generic-asm-offsets.h> > #include <generated/asm-offsets.h> > > +/* > + * Define this to boot U-Boot from a 32-bit program which sets the GDT > + * differently. This can be used to boot directly from coreboot, for example. > + * This is only useful for development. > + */ > +#undef LOAD_FROM_32_BIT > + > .section .text > .code32 > .globl _start > @@ -68,6 +75,10 @@ _start: > /* Save table pointer */ > movl %ecx, %esi > > +#ifdef LOAD_FROM_32_BIT > + lgdt gdt_ptr2 > +#endif > + > /* Load the segement registers to match the GDT loaded in start16.S */ > movl $(X86_GDT_ENTRY_32BIT_DS * X86_GDT_ENTRY_SIZE), %eax > movw %ax, %fs > @@ -220,3 +231,71 @@ multiboot_header: > .long 0 > /* entry addr */ > .long CONFIG_SYS_TEXT_BASE > + > +#ifdef LOAD_FROM_32_BIT > + /* > + * The following Global Descriptor Table is just enough to get us into > + * 'Flat Protected Mode' - It will be discarded as soon as the final > + * GDT is setup in a safe location in RAM > + */ > +gdt_ptr2: > + .word 0x1f /* limit (31 bytes = 4 GDT entries - 1) */ > + .long gdt_rom2 /* base */ > + > + /* Some CPUs are picky about GDT alignment... */ > + .align 16 > +.globl gdt_rom2 > +gdt_rom2: > + /* > + * The GDT table ... > + * > + * Selector Type > + * 0x00 NULL > + * 0x08 Unused > + * 0x10 32bit code > + * 0x18 32bit data/stack > + */ > + /* The NULL Desciptor - Mandatory */ > + .word 0x0000 /* limit_low */ > + .word 0x0000 /* base_low */ > + .byte 0x00 /* base_middle */ > + .byte 0x00 /* access */ > + .byte 0x00 /* flags + limit_high */ > + .byte 0x00 /* base_high */ > + > + /* Unused Desciptor - (matches Linux) */ > + .word 0x0000 /* limit_low */ > + .word 0x0000 /* base_low */ > + .byte 0x00 /* base_middle */ > + .byte 0x00 /* access */ > + .byte 0x00 /* flags + limit_high */ > + .byte 0x00 /* base_high */ > + > + /* > + * The Code Segment Descriptor: > + * - Base = 0x00000000 > + * - Size = 4GB > + * - Access = Present, Ring 0, Exec (Code), Readable > + * - Flags = 4kB Granularity, 32-bit > + */ > + .word 0xffff /* limit_low */ > + .word 0x0000 /* base_low */ > + .byte 0x00 /* base_middle */ > + .byte 0x9b /* access */ > + .byte 0xcf /* flags + limit_high */ > + .byte 0x00 /* base_high */ > + > + /* > + * The Data Segment Descriptor: > + * - Base = 0x00000000 > + * - Size = 4GB > + * - Access = Present, Ring 0, Non-Exec (Data), Writable > + * - Flags = 4kB Granularity, 32-bit > + */ > + .word 0xffff /* limit_low */ > + .word 0x0000 /* base_low */ > + .byte 0x00 /* base_middle */ > + .byte 0x93 /* access */ > + .byte 0xcf /* flags + limit_high */ > + .byte 0x00 /* base_high */ > +#endif > -- Regards, Bin _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
