Re: [PATCH v5 2/7] iommu: Decouple iommu_present() from bus ops

[Baolu Lu]

On 2023/10/12 20:37, Jason Gunthorpe wrote:
> On Thu, Oct 12, 2023 at 12:40:01PM +0100, Robin Murphy wrote:
> > On 2023-10-12 07:05, Baolu Lu wrote:
> > > On 10/12/23 2:14 AM, Robin Murphy wrote:
> > > > Much as I'd like to remove iommu_present(), the final remaining users
> > > > are proving stubbornly difficult to clean up, so kick that can down the
> > > > road and just rework it to preserve the current behaviour without
> > > > depending on bus ops. Since commit 57365a04c921 ("iommu: Move bus setup
> > >
> > > The iommu_present() is only used in below two drivers.
> > >
> > > $ git grep iommu_present
> > > drivers/gpu/drm/mediatek/mtk_drm_drv.c: if
> > > (!iommu_present(&platform_bus_type))
> > > drivers/gpu/drm/tegra/drm.c:    if (host1x_drm_wants_iommu(dev) &&
> > > iommu_present(&platform_bus_type)) {
> > >
> > > Both are platform drivers and have the device pointer passed in. Just
> > > out of curiosity, why not replacing them with device_iommu_mapped()
> > > instead? Sorry if I overlooked previous discussion.
> >
> > Yes, we've already gone round in circles on this several times, that's why
> > it's explicitly called out as "stubbornly difficult" in the commit message.
> > The Mediatek one is entirely redundant, but it seems I have yet to figure
> > out the right CC list to get anyone to care about that patch[1].

I see now. Thanks for the explanation.

> Please just have Joerg take such a trivial patch, there is no reason
> we need to torture outselves because DRM side is not behaving well. :(

I was not object to the patch. Just want to make sure that I understand
the reason why device_iommu_mapped() can't be used in those two drivers.

It's fine to me. I will add my r-b.

Best regards,
baolu