[U-Boot] [PATCH] x86: Use microcode update from device tree for all processors

[Ivan Gorinov]

Hi Bin,

On Wed, Apr 18, 2018 at 06:48:59AM -0600, Bin Meng wrote:
> >> I don't understand what the bug is here. The AP microcode update is
> >> done in sipi_vector.S.
> >
> > I have found how it works. When a ROM image is built, the binman tool
> > looks for symbol '_dt_ucode_base_size' and updates position and size
> > of the microcode update data in the ucode_base and ucode_size variables.
> > The ucode_base pointer is used to update the bootstrap CPU very early,
> > and the other CPUs later in the multiprocessing code.
> >
> > On x86, binman is called from Makefile only if a ROM image is created:
> >
> >     u-boot.rom: u-boot-x86-16bit.bin u-boot.bin \
> >     ...
> >         $(call if_changed,binman)
> >
> > If there is no ROM image, ucode_base and ucode_size are not initialized and
> > the microcode update data from DTB applied by microcode_update_intel() to the
> > bootstrap CPU is not used by the multiprocessing code.
> 
> Correct. If it's not a ROM image, which means U-Boot is probably not
> the 1st stage bootloader, which means updating microcode is not
> necessary. So is there any issue with current implementation?

If the 1st stage bootloader is running from the on-chip SRAM, there may be
not enough space to include the microcode update data. In this case, U-Boot
is a secondary boot loader but still has to update the microcode.