Re: [PATCH v8 02/11] iommu: Add max_pasids field in struct dev_iommu

[Baolu Lu]

On 2022/6/10 17:01, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Friday, June 10, 2022 2:47 PM
> >
> > On 2022/6/10 03:01, Raj, Ashok wrote:
> > > On Tue, Jun 07, 2022 at 09:49:33AM +0800, Lu Baolu wrote:
> > > > @@ -218,6 +219,30 @@ static void dev_iommu_free(struct device *dev)
> > > >    	kfree(param);
> > > >    }
> > > >
> > > > +static u32 dev_iommu_get_max_pasids(struct device *dev)
> > > > +{
> > > > +	u32 max_pasids = dev->iommu->iommu_dev->max_pasids;
> > > > +	u32 num_bits;
> > > > +	int ret;
> > > > +
> > > > +	if (!max_pasids)
> > > > +		return 0;
> > > > +
> > > > +	if (dev_is_pci(dev)) {
> > > > +		ret = pci_max_pasids(to_pci_dev(dev));
> > > > +		if (ret < 0)
> > > > +			return 0;
> > > > +
> > > > +		return min_t(u32, max_pasids, ret);
> > >
> > > Ah.. that answers my other question to consider device pasid-max. I guess
> > > if we need any enforcement of restricting devices that aren't supporting
> > > the full PASID, that will be done by some higher layer?
> >
> > The mm->pasid style of SVA is explicitly enabled through
> > iommu_dev_enable_feature(IOMMU_DEV_FEAT_SVA). The IOMMU driver
> > specific
> > restriction might be put there?
> >
> > > too many returns in this function, maybe setup all returns to the end of
> > > the function might be elegant?
> >
> > I didn't find cleanup room after a quick scan of the code. But sure, let
> > me go through code again offline.
>
> If we do care:
>
> +static u32 dev_iommu_get_max_pasids(struct device *dev)
> +{
> +	u32 max_pasids = 0,
> +	u32 num_bits = 0;
> +	int ret;
> +
> +	if (dev_is_pci(dev)) {
> +		ret = pci_max_pasids(to_pci_dev(dev));
> +		if (ret > 0)
> +			max_pasids = ret;
> +	} else {
> +		ret = device_property_read_u32(dev, "pasid-num-bits", &num_bits);
> +		if (!ret)
> +			max_pasids = 1UL << num_bits;
> +	}
> +
> +	return min_t(u32, max_pasids, dev->iommu->iommu_dev->max_pasids);
> +}

Great! Cleaner and more compact than mine. Thank you!

Best regards,
baolu