Re: [PATCH v2] iommu/amd: Make PerfOpt compulsory

[Mario Limonciello]

On 9/30/26 04:38, Vasant Hegde wrote:
> Mario,
>
> On 9/29/2026 7:04 AM, Mario Limonciello (AMD) wrote:
> > PerfOpt is only a feature usable by integrated GPUs and only in identity
> > mode.  Instead of leaving a policy knob in amdgpu, just turn it on when
> > an integrated GPU is in identity.
> >
> > This drops quite a bit of compatibility glue.  There was a refcounting
> > system, exported symbols, and device attach/detach logic.  By just setting
> > it immediately it's a lot more straightforward.
> >
> > Suggested-by: Jason Gunthorpe <jgg@xxxxxxxx>
> > Signed-off-by: Mario Limonciello (AMD) <superm1@xxxxxxxxxx>
> > ---
> > v2:
> >   * Move WARN_ON to amd_iommu_perfopt_clear()
> >   * Make amd_iommu_perfopt_clear() void
> >   * Drop unnecessary cleanup/create paths that unset feature
> >   * Enable the feature in IOMMU if supported (per guidance in IVRS spec)
> >   * Use existing check_feature() helper instead
> > ---
>
>
> .../...
>
> > diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> > index c9b28e5e582ea..a1adb40d5b79d 100644
> > --- a/drivers/iommu/amd/iommu.c
> > +++ b/drivers/iommu/amd/iommu.c
> > @@ -2345,6 +2345,35 @@ static void pdom_detach_iommu(struct amd_iommu *iommu,
> >   	spin_unlock_irqrestore(&pdom->lock, flags);
> >   }
> >   
> > +/*
> > + * Program or clear the per-IOMMU PerfOpt enable bit
> > + * This allows a privileged internal GPU to be able to bypass IOMMU when
> > + * in identity mode.
> > + */
> > +int amd_iommu_perfopt_set(struct amd_iommu *iommu, bool enable)
>
> Please move this to init.c file

Thanks, good suggestion.

> > +{
> > +	u32 old, val, readback;
> > +
> > +	if (!check_feature(FEATURE_PERF_OPT))
> > +		return enable ? -ENODEV : 0;
> > +
> > +	old = readl(iommu->mmio_base + MMIO_PERF_OPT_OFFSET);
> > +	if (old == U32_MAX)
> > +		return -EIO;
> > +
> > +	val = enable ? old | PERF_OPT_EN : old & ~PERF_OPT_EN;
> > +	if (val != old)
> > +		writel(val, iommu->mmio_base + MMIO_PERF_OPT_OFFSET);
> > +	readback = readl(iommu->mmio_base + MMIO_PERF_OPT_OFFSET);
> > +	if (readback == U32_MAX ||
> > +	    (readback & PERF_OPT_EN) != (val & PERF_OPT_EN)) {
> > +		dev_err(iommu->iommu.dev, "Failed to set PerfOpt to %d\n", enable);
> > +		return -EIO;
> > +	}
> > +
>
> May be check return value before enabling dev_data->perfopt?

I thought about this.

Let me know what you think of the approach of clearing the bit in 
amd_iommu_efr on failures within amd_iommu_perfopt_set().

That would mean that dev_data->perfopt doesn't get enabled later.