Re: How to synchronize CPUs on MMIO read?

[Alex Bennée]

Igor Lesik <lesikigor@meta.com> writes:

> Hi.
>
> I need to model some custom HW that synchronizes CPUs when they read MMIO 
> register N: MMIO read does not
> return until another CPU writes to MMIO register M. I modeled this behavior 
> with a) on MMIO read of N, save CPU into
> a list of waiting CPUs and put it asleep with cpu_interrupt(current_cpu, 
> CPU_INTERRUPT_HALT) and b) on MMIO write
> to M, wake all waiting CPUs with cpu->halted = 0; qemu_cpu_kick(cpu). It 
> seems to work fine. However, this HW has a
> twist: MMIO read of N returns a value that was written by MMIO write to M. 
> Can anyone please advise how this could
> be done?

Under TCG all MMIO accesses should be serialised by the BQL so no other
MMIO access can be taking place until you finish the operation.

>
>  
>
> Thanks!
>
> Igor


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro