Re: [PATCH v3 30/39] xen/riscv: implement APLIC-IMSIC-hart sync barrier for vCPU migration

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

On 11/5/26 4:32 PM, Baptiste Le Duc wrote:
> On 2026-11-05 15:21 +0100, Oleksii Kurochko wrote:
>> [ ... 348 lines skipped ... ]
>>> LGTM, but I wonder why, as I said in the original patch, sync_id is
>>> really needed.
>>>
>>
>> I think that I am not understand your response. Could you please
>> re-phrase it?
> I'm questionning the need of the sync_id field as it will always be
> equal to imsic_cfg.nr_ids, couldn't we drop it?
> 

It's equal to nr_ids by choice rather than by necessity: which identity
gets reserved is decided in a single place, imsic_parse_node(), and all
the users (the genmsi write, the pending bit the barrier spins on, the
limit on the APLIC sources and the ASSERT() in imsic_irq_enable()) refer
to it by its role rather than as "the last identity".

Basically if one day someone will decide to come up with EIID allocator 
instead of using static allocation then it will be harder to find a 
places where to change.

So yes, it could be drooped but at the moment I think it is useful to 
have separate field or ,at least, as an option in asm/imsic.h:

static inline unsigned int imsic_sync_id(const struct imsic_config *cfg)
{
     return cfg->nr_ids;
}

~ Oleksii