On Thu, 2022-06-23 at 19:44 -0700, Nicolin Chen wrote:
> On Fri, Jun 24, 2022 at 09:35:49AM +0800, Baolu Lu wrote:
> > External email: Use caution opening links or attachments
> >
> >
> > On 2022/6/24 04:00, Nicolin Chen wrote:
> > > diff --git a/drivers/iommu/mtk_iommu_v1.c
> > > b/drivers/iommu/mtk_iommu_v1.c
> > > index e1cb51b9866c..5386d889429d 100644
> > > --- a/drivers/iommu/mtk_iommu_v1.c
> > > +++ b/drivers/iommu/mtk_iommu_v1.c
> > > @@ -304,7 +304,7 @@ static int mtk_iommu_v1_attach_device(struct
> > > iommu_domain *domain, struct device
> > > /* Only allow the domain created internally. */
> > > mtk_mapping = data->mapping;
> > > if (mtk_mapping->domain != domain)
> > > - return 0;
> > > + return -EMEDIUMTYPE;
> > >
> > > if (!data->m4u_dom) {
> > > data->m4u_dom = dom;
> >
> > This change looks odd. It turns the return value from success to
> > failure. Is it a bug? If so, it should go through a separated fix
> > patch.
Thanks for the review:)
>
> Makes sense.
>
> I read the commit log of the original change:
>
https://lore.kernel.org/r/1589530123-30240-1-git-send-email-yong.wu@xxxxxxxxxxxx
>
> It doesn't seem to allow devices to get attached to different
> domains other than the shared mapping->domain, created in the
> in the mtk_iommu_probe_device(). So it looks like returning 0
> is intentional. Though I am still very confused by this return
> value here, I doubt it has ever been used in a VFIO context.
It's not used in VFIO context. "return 0" just satisfy the iommu
framework to go ahead. and yes, here we only allow the shared "mapping-
>domain" (All the devices share a domain created internally).
thus I think we should still keep "return 0" here.
Thanks:)
>
> Young, would you please give us some input?
>
> Overall, I feel it's better to play it safe here by dropping
> this part. If we later confirm there is a need to fix it, we
> will do that in a separate patch anyway.
>
> Thanks
> Nic
