Re: [PATCH 3/7] iommu/vt-d: Support Enhanced Command Interface

[Baolu Lu]

On 2023/1/13 21:55, Baolu Lu wrote:
> > +/*
> > + * Function to submit a command to the enhanced command interface. The
> > + * valid enhanced command descriptions are defined in Table 47 of the
> > + * VT-d spec. The VT-d hardware implementation may support some but not
> > + * all commands, which can be determined by checking the Enhanced
> > + * Command Capability Register.
> > + *
> > + * Return values:
> > + *  - 0: Command successful without any error;
> > + *  - Negative: software error value;
> > + *  - Nonzero positive: failure status code defined in Table 48.
> > + */
> > +int ecmd_submit_sync(struct intel_iommu *iommu, u8 ecmd,
> > +             u64 oa, bool has_ob, u64 ob)
> > +{
> > +    unsigned long flags;
> > +    u64 res;
> > +    int ret;
> > +
> > +    if (!cap_ecmds(iommu->cap))
> > +        return -ENODEV;
> > +
> > +    raw_spin_lock_irqsave(&iommu->register_lock, flags);
> > +
> > +    res = dmar_readq(iommu->reg + DMAR_ECRSP_REG);
> > +    if (res & DMA_ECMD_ECRSP_IP) {
> > +        ret = -EBUSY;
> > +        goto err;
> > +    }
> > +
> > +    if (has_ob)
> > +        dmar_writeq(iommu->reg + DMAR_ECEO_REG, ob);
>
> The ecmds that require a Operand B are statically defined in the spec,
> right? What will it look like if we define a static ignore_ob(ecmd)?

Or simply remove has_ob parameter? The least case is an unnecessary
write to a register. It's fine as far as I can see since we should avoid
using it in any critical path.

--
Best regards,
baolu