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>>> + >>> +    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(). Yeah. It makes sense. -Vasant