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

[Ivan Gorinov]

On Thu, Apr 05, 2018 at 09:31:34AM -0600, Bin Meng wrote:
> > The microcode update data block encoded in Device Tree is used by
> > the bootstrap processor (BSP) but not passed to the other CPUs (AP).
> 
> 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.