From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ivan Gorinov <ivan.gorinov@intel.com>
Date: Tue, 17 Apr 2018 11:29:56 -0700
Subject: [U-Boot] [PATCH] x86: Use microcode update from device tree for
 all processors
In-Reply-To: <CAEUhbmVmPNQU0tgsn7y29d26dr-7sZWP_50i1zXC4ozxBe7pwA@mail.gmail.com>
References: <20180404230700.GA57192@intel.com>
 <CAEUhbmVmPNQU0tgsn7y29d26dr-7sZWP_50i1zXC4ozxBe7pwA@mail.gmail.com>
Message-ID: <20180417182956.GA57575@intel.com>
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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.