On Thu, Jan 05, 2017 at 01:52:29PM +0000, Robin Murphy wrote:
[...]
> > Question: I had a look into this and instead of fiddling about with the
> > linker script entries in ACPI (ie IORT_ACPI_DECLARE - which I hope this
> > patchset would help remove entirely), I think that the only check we
> > need in IORT is, depending on what type of SMMU a given device is
> > connected to, to check if the respective SMMU driver is compiled in the
> > kernel and it will be probed, _eventually_.
> >
> > As Robin said, by the time a device is probed the respective SMMU
> > devices are already created and registered with IORT kernel code or
> > they will never be, so to understand if we should defer probing
> > SMMU device creation is _not_ really a problem in ACPI.
> >
> > To check if a SMMU driver is enabled, do we really need a linker
> > table ?
> >
> > Would not a check based on eg:
> >
> > /**
> > * @type: IOMMU IORT node type of the IOMMU a device is connected to
> > */
> > static bool iort_iommu_driver_enabled(u8 type)
> > {
> > switch (type) {
> > case ACPI_IORT_SMMU_V3:
> > return IS_ENABLED(CONFIG_ARM_SMMU_V3);
>
> IS_BUILTIN(...)
Yep right, it is currently equivalent but that does not mean it
will always be.
> > case ACPI_IORT_SMMU:
> > return IS_ENABLED(CONFIG_ARM_SMMU);
> > default:
> > pr_warn("Unknown IORT SMMU type\n");
>
> Might displaying the actual value be helfpul for debugging a broken IORT
> table?
Yes I will do.
> > return false;
> > }
> > }
> >
> > be sufficient (it is a bit gross, agreed, but it is to understand if
> > that's all we need) ? Is there anything I am missing ?
> >
> > Let me know, I will put together a patch for you I really do not
> > want to block your series for this trivial niggle.
>
> Other than that, though, I like it :) IORT has a small, strictly
> bounded, set of supported devices, so I really don't see the need to go
> overboard putting it on parity with DT when something this neat and
> simple will suffice.
Ok, patch coming, which will also allow Sricharan to get rid of the
IORT linker script infrastructure altogether (and more than that,
I can write the patches on top of Sricharan series that I managed
to rebase against v4.10-rc2).
Thanks,
Lorenzo
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