[PATCH] lib: sbi: Add option to select boot hart

[Jessica Clarke]

On 30 Nov 2022, at 03:33, WeiLiang Lim <weiliang.lim at starfivetech.com> wrote:
> 
>> -----Original Message-----
>> From: Jessica Clarke <jrtc27 at jrtc27.com>
>> Sent: Wednesday, November 30, 2022 12:18 AM
>> To: WeiLiang Lim <weiliang.lim at starfivetech.com>
>> Cc: opensbi at lists.infradead.org; Cheehong Ang
>> <cheehong.ang at starfivetech.com>; JunLiang Tan
>> <junliang.tan at starfivetech.com>
>> Subject: Re: [PATCH] lib: sbi: Add option to select boot hart
>> 
>> On 29 Nov 2022, at 05:21, Wei Liang Lim <weiliang.lim at starfivetech.com>
>> wrote:
>>> 
>>> In certain scenario, user needs to select a particular hart ID as the boot hart.
>> This option provide the flexibility for user to select the preferred boot hart.
>> 
>> Why? What’s wrong with the others?
>> 
>> Jess
>> 
> We need this patch for 2 scenarios below:
> 1) On our architecture, there are some harts supporting MMU sv39/sv48 and some harts only supporting sv39. When those harts with sv48 support is picked as boot hart, the OS automatically assumes all the other non-boot harts support sv48 as well. Therefore, we need to select the harts with sv39 supports only as the boot hart to avoid the incorrect page table issues in non-boot harts.

If you have a heterogenous environment then this isn’t the right fix,
OSes need to be aware of heterogeneity otherwise other things can
easily go wrong. And if they’re aware of that then you don’t need to
control which OS boots. Nothing in the RISC-V world currently says that
OSes should do their feature detection on the first hart that boots...

> 2) We have use case which requires the same boot hart to save OS context before going into 'hibernation' mode and to restore the OS context after resuming from 'hibernation' mode.

I can’t imagine current OpenSBI+Linux is at all prepared for
hibernation so don’t think that’s a sufficient justification for it
today?

Jess

>>> Signed-off-by: Wei Liang Lim <weiliang.lim at starfivetech.com>
>>> Reviewed-by: Chee Hong Ang <cheehong.ang at starfivetech.com>
>>> Reviewed-by: Jun Liang Tan <junliang.tan at starfivetech.com>
>>> ---
>>> firmware/objects.mk | 4 ++++
>>> lib/sbi/sbi_init.c  | 9 ++++++++-
>>> 2 files changed, 12 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/firmware/objects.mk b/firmware/objects.mk index
>>> a1704c4..2b41718 100644
>>> --- a/firmware/objects.mk
>>> +++ b/firmware/objects.mk
>>> @@ -28,6 +28,10 @@ ifdef FW_TEXT_START firmware-genflags-y +=
>>> -DFW_TEXT_START=$(FW_TEXT_START) endif
>>> 
>>> +ifdef FW_BOOT_HART_ID
>>> +firmware-genflags-y += -DFW_BOOT_HART_ID=$(FW_BOOT_HART_ID)
>>> +endif
>>> +
>>> ifdef FW_FDT_PATH
>>> firmware-genflags-y += -DFW_FDT_PATH=\"$(FW_FDT_PATH)\"
>>> ifdef FW_FDT_PADDING
>>> diff --git a/lib/sbi/sbi_init.c b/lib/sbi/sbi_init.c index
>>> d57efa7..5abfa79 100644
>>> --- a/lib/sbi/sbi_init.c
>>> +++ b/lib/sbi/sbi_init.c
>>> @@ -443,7 +443,9 @@ static void __noreturn init_warmboot(struct
>> sbi_scratch *scratch, u32 hartid)
>>> 			     scratch->next_mode, FALSE);
>>> }
>>> 
>>> +#ifndef FW_BOOT_HART_ID
>>> static atomic_t coldboot_lottery = ATOMIC_INITIALIZER(0);
>>> +#endif
>>> 
>>> /**
>>> * Initialize OpenSBI library for current HART and jump to next @@
>>> -494,7 +496,12 @@ void __noreturn sbi_init(struct sbi_scratch *scratch)
>>> 	 * HARTs which satisfy above condition.
>>> 	 */
>>> 
>>> -	if (next_mode_supported && atomic_xchg(&coldboot_lottery, 1) == 0)
>>> +	if (next_mode_supported &&
>>> +#ifdef FW_BOOT_HART_ID
>>> +		hartid == FW_BOOT_HART_ID)
>>> +#else
>>> +		atomic_xchg(&coldboot_lottery, 1) == 0) #endif
>>> 		coldboot = TRUE;
>>> 
>>> 	/*
>>> --
>>> 2.25.1
>>> 
>>> 
>>> --
>>> opensbi mailing list
>>> opensbi at lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/opensbi
>