[U-Boot] Hart lottery and CONFIG_XIP

[Troy Benjegerdes]

> On Jun 2, 2019, at 9:22 PM, Rick Chen <rickchen36 at gmail.com> wrote:
> 
> Hi Troy
> 
>>> From: Troy Benjegerdes [mailto:troy.benjegerdes at sifive.com]
>>> Sent: Saturday, June 01, 2019 12:24 AM
>>> To: Auer, Lukas
>>> Cc: Rick Jian-Zhi Chen(陳建志); bmeng.cn at gmail.com; palmer at sifive.com
>>> Subject: Re: Hart lottery and CONFIG_XIP
>>> 
>>> 
>>> 
>>>> On May 31, 2019, at 9:13 AM, Auer, Lukas <lukas.auer at aisec.fraunhofer.de>
>>> wrote:
>>>> 
>>>> Hi Troy,
>>>> 
>>>> On Fri, 2019-05-31 at 08:18 -0500, Troy Benjegerdes wrote:
>>>>> Wouldn't the following line in head.S fail when running from flash
>>>>> (although maybe not in a way that prevents booting)
>>>>> 
>>>>>       /* save the boot hart id to global_data */
>>>>>       SREG    tp, GD_BOOT_HART(gp)
>>>>> 
>>>>> Shouldn’t this be protected by CONFIG_XIP?
>>>> 
>>>> The boot hart ID is stored in global data, which is allocated from the
>>>> stack (in board_init_f_alloc_reserve() ). It is therefore writable and
>>>> won't cause any issues when running from flash.
>>> 
>>> Sorry about the confusion, I was reading it wrong earlier.
>>> 
>>> I’m hoping to have a couple of patches ready later today to change the
>>> CONFIG_XIP patch to ‘CONFIG_HART_LOTTERY’ since it is also useful to
>>> remove the potential indeterminism of which hart wins the lottery when doing
>>> board bringup and debugging.
> 
> I am OK with that.
> Actually my preliminary patch about
> [PATCH 0/4] AE350 support SMP boot from flash
> did as your wish.
> 
> You can refer it :
> [PATCH 1/4] riscv: hart_lottery and available harts feature can be seletable
> https://www.mail-archive.com/u-boot@lists.denx.de/msg323419.html
> 
> Rick

To follow up on https://www.mail-archive.com/u-boot@lists.denx.de/msg323526.html

It is confusing and misleading to mix CONFIG_XIP and CONFIG_HART_LOTTERY.

From an system testing and validation point of view, I would find it much better
(especially at very early boot stages, where U-boot might be the first non-ROM code
running) to have a deterministic process to determine what core runs U-boot. This 
necessarily seems as it will require a CONFIG_BOOT_HART option, as we are not
in a position to parse a device tree in head.S