[PATCH v2 02/11] RISC-V: make RISCV_SBI and RISCV_M_MODE explicitly mutually exclusive

[Ahmad Fatoum]

Hello Antony,

On 07.05.21 16:25, Antony Pavlov wrote:
>> I would really like to have a riscv{32,64}_defconfig that can just build all boards
>> at once. Do you know if this could be dynamically determined?
> 
> At the moment I have not answer.
> I'll try to investigate dynamic mode determination, it's very attractive idea.
> 
> On the other hand compile time mode selection is not the show stopper for
> "one defconfig to build them all": we have to make STACK_SIZE and MALLOC_SIZE
> per-board parameters not per-defconfig parameters like now.
> 
> If we could make STACK_SIZE and MALLOC_SIZE per-board compile-time parameters then
> we can make RISC-V mode per-board compile-time parameter too. Is this solution
> acceptable?

MALLOC_SIZE can be set as 0 and barebox will determine it based on
membase + memsize that are set by PBL.

STACK_SIZE must be set per Kconfig, but I think even a generous default stack
size should accommodate all targets.

If we do the same for RISC-V mode that would probably mean having
two functions barebox_riscv_machine_entry() and barebox_riscv_supervisor_entry()
in PBL that take care to pass the correct info to barebox proper.

Apparently, you can determine mode if you catch exceptions:
https://forums.sifive.com/t/how-to-determine-the-current-execution-privilege-mode/2823

We don't yet install exception handlers in barebox, but I am fine with using
different PBL common code entry functions.

What do you think?

Cheers,
Ahmad

> 
>>> +
>>>  source "arch/riscv/Kconfig.socs"
>>>  
>>>  config CPU_SUPPORTS_32BIT_KERNEL
>>> @@ -97,14 +109,4 @@ config NMON_HELP
>>>  	  Say yes here to get the nmon commands message on
>>>  	  every nmon start.
>>>  
>>> -# set if we run in machine mode, cleared if we run in supervisor mode
>>> -config RISCV_M_MODE
>>> -	bool
>>> -
>>> -# set if we are running in S-mode and can use SBI calls
>>> -config RISCV_SBI
>>> -	bool
>>> -	depends on !RISCV_M_MODE
>>> -	default y
>>> -
>>>  endmenu
>>> diff --git a/arch/riscv/Kconfig.socs b/arch/riscv/Kconfig.socs
>>> index c6875738d0..f767942f34 100644
>>> --- a/arch/riscv/Kconfig.socs
>>> +++ b/arch/riscv/Kconfig.socs
>>> @@ -3,10 +3,10 @@ menu "SoC selection"
>>>  config SOC_ERIZO
>>>  	bool "Erizo SoC"
>>>  	depends on ARCH_RV32I
>>> +	depends on RISCV_M_MODE
>>>  	select HAS_ASM_DEBUG_LL
>>>  	select HAS_NMON
>>>  	select USE_COMPRESSED_DTB
>>> -	select RISCV_M_MODE
>>>  	select RISCV_TIMER
>>>  
>>>  config BOARD_ERIZO_GENERIC
>>> @@ -15,6 +15,7 @@ config BOARD_ERIZO_GENERIC
>>>  
>>>  config SOC_VIRT
>>>  	bool "QEMU Virt Machine"
>>> +	depends on RISCV_SBI
>>>  	select BOARD_RISCV_GENERIC_DT
>>>  	select CLINT_TIMER
>>>  	help
>>> @@ -23,6 +24,7 @@ config SOC_VIRT
>>>  
>>>  config SOC_SIFIVE
>>>  	bool "SiFive SoCs"
>>> +	depends on RISCV_SBI
>>>  	select CLK_SIFIVE
>>>  	select CLK_SIFIVE_PRCI
>>>  	select RISCV_TIMER
>>> diff --git a/arch/riscv/configs/erizo_generic_defconfig b/arch/riscv/configs/erizo_generic_defconfig
>>> index 247a179130..16168eef66 100644
>>> --- a/arch/riscv/configs/erizo_generic_defconfig
>>> +++ b/arch/riscv/configs/erizo_generic_defconfig
>>> @@ -1,3 +1,4 @@
>>> +CONFIG_RISCV_M_MODE=y
>>>  CONFIG_SOC_ERIZO=y
>>>  # CONFIG_GLOBALVAR is not set
>>>  CONFIG_STACK_SIZE=0x20000
>>>
>>
>> -- 
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> 
> 

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
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