• Masahiro Yamada's avatar
    ARM: uniphier: rework SMP operations to use trampoline code · b1e4006a
    Masahiro Yamada authored
    
    
    The complexity of the boot sequence of UniPhier SoC family is
    a PITA due to the following hardware limitations:
    
    [1] No dedicated on-chip SRAM
    SoCs in general have small SRAM, on which a tiny firmware or a boot
    loader can run before SDRAM is initialized.  As UniPhier SoCs do not
    have any dedicated SRAM accessible from CPUs, the locked outer cache
    is used instead.  Due to the ARM specification, to have access to
    the outer cache, the MMU must be enabled.  This is done for all CPU
    cores by the program hard-wired in the boot ROM.  The boot ROM code
    loads a small amount of program (this is usually SPL of U-Boot) from
    a non-volatile device onto the locked outer cache, and the primary
    CPU jumps to it.  The secondary CPUs stay in the boot ROM until they
    are kicked by the primary CPU.
    
    [2] CPUs can not directly jump to SDRAM address space
    As mentioned above, the MMU is enable for all the CPUs with the page
    table hard-wired in the boot ROM.  Unfortunately, the page table only
    has minimal sets of valid sections; all the sections of SDRAM address
    space are zero-filled.  That means all the CPUs, including secondary
    ones, can not jump directly to SDRAM address space.  So, the primary
    CPU must bring up secondary CPUs to accessible address mapped onto
    the outer cache, then again kick them to SDRAM address space.
    
    Before this commit, this complex task was done with help of a boot
    loader (U-Boot); U-Boot SPL brings up the secondary CPUs to the entry
    of U-Boot SPL and they stay there until they are kicked by Linux.
    This is not nice because a boot loader must put the secondary CPUs
    into a certain state expected by the kernel.  It makes difficult to
    port another boot loader because the boot loader and the kernel must
    work in sync to wake up the secondary CPUs.
    
    This commit reworks the SMP operations so that they do not rely on
    particular boot loader implementation; the SMP operations (platsmp.c)
    put trampoline code (headsmp.S) on a locked way of the outer cache.
    The secondary CPUs jump from the boot ROM to secondary_entry via the
    trampoline code.  The boot loader no longer needs to take care of SMP.
    Signed-off-by: Masahiro Yamada's avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    Signed-off-by: default avatarOlof Johansson <olof@lixom.net>
    b1e4006a
Makefile 63 Bytes