Re: [PATCH v3 13/13] iommu/arm-smmu-v3: Add support for PCI PASID

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Wed, Dec 18, 2019 at 11:17:55AM +0100, Auger Eric wrote:
> > +static int arm_smmu_enable_pasid(struct arm_smmu_master *master)
> > +{
> > +	int ret;
> > +	int features;
> > +	int num_pasids;
> > +	struct pci_dev *pdev;
> > +
> > +	if (!dev_is_pci(master->dev))
> > +		return -ENODEV;
> > +
> > +	pdev = to_pci_dev(master->dev);
> > +
> > +	features = pci_pasid_features(pdev);
> > +	if (features < 0)
> > +		return -ENODEV;
> why -ENODEV?

Right that should return features. The below should return num_pasids.

> > +
> > +	num_pasids = pci_max_pasids(pdev);
> > +	if (num_pasids <= 0)
> > +		return -ENODEV;
> > +
> > +	ret = pci_enable_pasid(pdev, features);
> > +	if (!ret)
> > +		master->ssid_bits = min_t(u8, ilog2(num_pasids),
> > +					  master->smmu->ssid_bits);
> so here we are ;-)
> > +	return ret;
> > +}
> > +
> > +static void arm_smmu_disable_pasid(struct arm_smmu_master *master)
> > +{
> > +	struct pci_dev *pdev;
> > +
> > +	if (!dev_is_pci(master->dev))
> > +		return;
> > +
> > +	pdev = to_pci_dev(master->dev);
> > +
> > +	if (!pdev->pasid_enabled)
> > +		return;
> > +
> > +	master->ssid_bits = 0;
> > +	pci_disable_pasid(pdev);
> > +}
> > +
> >  static void arm_smmu_detach_dev(struct arm_smmu_master *master)
> >  {
> >  	unsigned long flags;
> > @@ -2851,13 +2894,16 @@ static int arm_smmu_add_device(struct device *dev)
> >  
> >  	master->ssid_bits = min(smmu->ssid_bits, fwspec->num_pasid_bits);
> >  
> > +	/* Note that PASID must be enabled before, and disabled after ATS */
> > +	arm_smmu_enable_pasid(master);
> No error handling?

The device still works if PASID isn't supported or cannot be enabled, it
just won't have some capabilities (IOMMU_DEV_FEAT_AUX and
IOMMU_DEV_FEAT_SVA), so I don't think add_device should return an error.

But it's a good point, I think at least printing an error like
arm_smmu_enable_ats() does would be better.

Thanks,
Jean