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SubjectRe: [PATCH v5 2/8] iommu/vt-d: Add per-device IOMMU feature ops entries
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Hi Joerg,

On 1/11/19 7:16 PM, Joerg Roedel wrote:
>> +
>> +static bool
>> +intel_iommu_dev_has_feat(struct device *dev, enum iommu_dev_features feat)
>> +{
>> + struct device_domain_info *info = dev->archdata.iommu;
>> +
>> + if (feat == IOMMU_DEV_FEAT_AUX)
>> + return scalable_mode_support() && info && info->auxd_enabled;
>> +
>> + return false;
>> +}
> Why is this checking the auxd_enabled flag? The function should just
> return whether the device_supports_ scalable mode, not whether it is
> enabled.

Yes, as the API name implies, it should return the device capability
instead of enable/disable status. I misused this API in the IOMMU
driver.

Since we already have iommu_dev_enable/disable_feature() to enable and
disable an iommu specific feature, is it possible to add another API to
query whether a specific feature has been enabled?

How about

bool iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX)?

This is necessary for the third party drivers (like vfio) to determine
which domain attach interface it should use:

if (iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX))
iommmu_aux_attach_device(domain, dev)
else
iommu_attach_device(domain, dev)


Best regards,
Lu Baolu

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