[U-Boot] [PATCH v3 2/3] x86: fsp: Load GDT before calling FspInitEntry

[Simon Glass]

On 6 June 2015 at 21:33, Bin Meng <bmeng.cn at gmail.com> wrote:
> Currently the FSP execution environment GDT is setup by U-Boot in
> arch/x86/cpu/start16.S, which works pretty well. But if we try to
> move the FspInitEntry call a little bit later to better fit into
> U-Boot's initialization sequence, FSP will fail to bring up the AP
> due to #GP fault as AP's GDT is duplicated from BSP whose GDT is
> now moved into CAR, and unfortunately FSP calls AP initialization
> after it disables the CAR. So basically the BSP's GDT still refers
> to the one in the CAR, whose content is no longer available, so
> when AP starts up and loads its segment register, it blows up.
>
> To resolve this, we load GDT before calling into FspInitEntry.
> The GDT is the same one used in arch/x86/cpu/start16.S, which is
> in the ROM and exists forever.
>
> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> Tested-by: Andrew Bradford <andrew.bradford at kodakalaris.com>
> Tested-by: Simon Glass <sjg at chromium.org>
>
> ---
>
> Changes in v3:
> - Rename gdt in arch/x86/cpu/start16.S to gdt_rom
> - Change 'extern u32 gdt' to 'extern char gdt_rom[]'
> - Add comments to setup_fsp_gdt()

Acked-by: Simon Glass <sjg at chromium.org>