Re: [PATCH] LoongArch: KVM: Access mailbox directly in mail_send()

[Bibo Mao]

On 2025/7/31 下午5:30, Yanteng Si wrote:
> 在 7/31/25 3:59 PM, Bibo Mao 写道:
> > With function mail_send(), it is to write mailbox of other VCPUs.
> > Existing simple APIs read_mailbox/write_mailbox can be used directly
> > rather than send command on IOCSR address.
> Hmm, that's indeed a feasible approach. However, I'm
> curious: what is the purpose of designing IOCSR in
> LoongArch? Is it merely to make things "complicated"?

I am not chip designer -:). MMIO address space is ok from my side, 
however I do not know how to solve multi-chip problem with MMIO method.

Regards
Bibo Mao
> Thanks,
> Yanteng
> > Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> > ---
> >   arch/loongarch/kvm/intc/ipi.c | 16 +++++++++++++---
> >   1 file changed, 13 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/loongarch/kvm/intc/ipi.c 
> > b/arch/loongarch/kvm/intc/ipi.c
> > index fe734dc062ed..832b2d4aa2ef 100644
> > --- a/arch/loongarch/kvm/intc/ipi.c
> > +++ b/arch/loongarch/kvm/intc/ipi.c
> > @@ -134,7 +134,8 @@ static int send_ipi_data(struct kvm_vcpu *vcpu, 
> > gpa_t addr, uint64_t data)
> >   static int mail_send(struct kvm *kvm, uint64_t data)
> >   {
> > -    int cpu, mailbox, offset;
> > +    int i, cpu, mailbox, offset;
> > +    uint32_t val = 0, mask = 0;
> >       struct kvm_vcpu *vcpu;
> >       cpu = ((data & 0xffffffff) >> 16) & 0x3ff;
> > @@ -144,9 +145,18 @@ static int mail_send(struct kvm *kvm, uint64_t data)
> >           return -EINVAL;
> >       }
> >       mailbox = ((data & 0xffffffff) >> 2) & 0x7;
> > -    offset = IOCSR_IPI_BASE + IOCSR_IPI_BUF_20 + mailbox * 4;
> > +    offset = IOCSR_IPI_BUF_20 + mailbox * 4;
> > +    if ((data >> 27) & 0xf) {
> > +        val = read_mailbox(vcpu, offset, 4);
> > +        for (i = 0; i < 4; i++)
> > +            if (data & (BIT(27 + i)))
> > +                mask |= (0xff << (i * 8));
> > +        val &= mask;
> > +    }
> > -    return send_ipi_data(vcpu, offset, data);
> > +    val |= ((uint32_t)(data >> 32) & ~mask);
> > +    write_mailbox(vcpu, offset, val, 4);
> > +    return 0;
> >   }
> >   static int any_send(struct kvm *kvm, uint64_t data)
> >
> > base-commit: 038d61fd642278bab63ee8ef722c50d10ab01e8f