Re: [PATCH v4 1/3] iommu/tegra-smmu: Use fwspec in tegra_smmu_(de)attach_dev

Nicolin Chen
2020-10-02T23:59:33Z

On Fri, Oct 02, 2020 at 11:12:18PM +0300, Dmitry Osipenko wrote:
> 02.10.2020 22:45, Nicolin Chen пишет:
> > On Fri, Oct 02, 2020 at 05:41:50PM +0300, Dmitry Osipenko wrote:
> >> 02.10.2020 09:08, Nicolin Chen пишет:
> >>> static int tegra_smmu_attach_dev(struct iommu_domain *domain,
> >>> struct device *dev)
> >>> {
> >>> + struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> >>> struct tegra_smmu *smmu = dev_iommu_priv_get(dev);
> >>> struct tegra_smmu_as *as = to_smmu_as(domain);
> >>> - struct device_node *np = dev->of_node;
> >>> - struct of_phandle_args args;
> >>> unsigned int index = 0;
> >>> int err = 0;
> >>>
> >>> - while (!of_parse_phandle_with_args(np, "iommus", "#iommu-cells", index,
> >>> - &args)) {
> >>> - unsigned int swgroup = args.args[0];
> >>> -
> >>> - if (args.np != smmu->dev->of_node) {
> >>> - of_node_put(args.np);
> >>> - continue;
> >>> - }
> >>> -
> >>> - of_node_put(args.np);
> >>> + if (!fwspec)
> >>> + return -ENOENT;
> >>
> >> Could the !fwspec ever be true here as well?
> >
> > There are multiple callers of this function. It's really not that
> > straightforward to track every one of them. So I'd rather have it
> > here as other iommu drivers do. We are human beings, so we could
> > have missed something somewhere, especially callers are not from
> > tegra-* drivers.
> >
>
> I'm looking at the IOMMU core and it requires device to be in IOMMU
> group before attach_dev() could be called.
>
> The group can't be assigned to device without the fwspec, see
> tegra_smmu_device_group().
>
> Seems majority of IOMMU drivers are checking dev_iommu_priv_get() for
> NULL in attach_dev(), some not checking anything, some check both and
> only arm-smmu checks the fwspec.

As I said a couple of days ago, I don't like to assume that the
callers won't change. And this time, it's from open code. So I
don't want to assume that there won't be a change.

If you are confident that there is no need to add such a check,
please send patches to remove those checks in those drivers to
see if others would agree. I would be willing to remove it after
that. Otherwise, I'd like to keep this.

Thanks for the review.