[U-Boot] [PATCH 5/7] riscv: add support for multi-hart systems

[Auer, Lukas]

On Tue, 2019-02-12 at 01:48 +0000, Anup Patel wrote:
> > -----Original Message-----
> > From: Lukas Auer [mailto:lukas.auer at aisec.fraunhofer.de]
> > Sent: Tuesday, February 12, 2019 3:44 AM
> > To: u-boot at lists.denx.de
> > Cc: Atish Patra <Atish.Patra at wdc.com>; Anup Patel
> > <Anup.Patel at wdc.com>; Bin Meng <bmeng.cn at gmail.com>; Andreas
> > Schwab <schwab at suse.de>; Palmer Dabbelt <palmer at sifive.com>;
> > Alexander Graf <agraf at suse.de>; Lukas Auer
> > <lukas.auer at aisec.fraunhofer.de>; Anup Patel <anup at brainfault.org>;
> > Rick
> > Chen <rick at andestech.com>; Baruch Siach <baruch at tkos.co.il>; Stefan
> > Roese <sr at denx.de>
> > Subject: [PATCH 5/7] riscv: add support for multi-hart systems
> > 
> > On RISC-V, all harts boot independently. To be able to run on a
> > multi-hart
> > system, U-Boot must be extended with the functionality to manage
> > all harts
> > in the system. A new config option, CONFIG_MAIN_HART, is used to
> > select
> > the hart U-Boot runs on. All other harts are halted.
> > U-Boot can delegate functions to them using smp_call_function().
> > 
> > Every hart has a valid pointer to the global data structure and a
> > 8KiB stack by
> > default. The stack size is set with CONFIG_STACK_SIZE_SHIFT.
> > 
> > Signed-off-by: Lukas Auer <lukas.auer at aisec.fraunhofer.de>
> > ---
> > 
> >  arch/riscv/Kconfig           |  12 +++++
> >  arch/riscv/cpu/start.S       | 102
> > ++++++++++++++++++++++++++++++++++-
> >  arch/riscv/include/asm/csr.h |   1 +
> >  3 files changed, 114 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index
> > 3a51339c4d..af8d0f8d67 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -140,4 +140,16 @@ config SBI_IPI
> >  	default y if RISCV_SMODE
> >  	depends on SMP
> > 
> > +config MAIN_HART
> > +	int "Main hart in system"
> > +	default 0
> > +	help
> > +	  Some SoCs include harts of various sizes, some of which might
> > not
> > +	  be suitable for running U-Boot. CONFIG_MAIN_HART is used to
> > select
> > +	  the hart U-Boot runs on.
> 
> This config option can be avoided altogether if we have
> lottery based system to select "Main HART" in start.S.
> 
> With the MAIN_HART config option in-place, every system
> will have to pick a "Main HART". What if the "Main HART"
> itself does not come online due to HW failure.
> 

Good point, I did not consider this. I will add a lottery-based system
in the next version.

Thanks,
Lukas