Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Robin Murphy]

On 2022-09-27 16:29, Geert Uytterhoeven wrote:
> Hi Robin,
>
> On Tue, Sep 27, 2022 at 5:09 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > On 2022-09-27 15:48, Geert Uytterhoeven wrote:
> > > On Tue, Sep 27, 2022 at 4:15 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > > > On 2022-09-27 14:36, Geert Uytterhoeven wrote:
> > > > > There is no point in asking the user about both "Apple DART Formats" and
> > > > > "Apple DART IOMMU Support", as the former is useless without the latter,
> > > > > and the latter auto-selects the former.
> > > > >
> > > > > Fixes: 745ef1092bcfcf3b ("iommu/io-pgtable: Move Apple DART support to its own file")
> > > > > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> > > > > ---
> > > > > Should IOMMU_IO_PGTABLE_LPAE and IOMMU_IO_PGTABLE_ARMV7S be made
> > > > > invisible, too?
> > > > > Are there users that do not select them?
> > > >
> > > > The aim was for formats to be independently selectable for COMPILE_TEST
> > > > coverage. The Arm formats are manually selectable for the sake of their
> > > > runtime self-tests, which are self-contained, but since DART format
> > > > doesn't do anything by itself I'd agree there's no need to prompt when
> > > > !COMPILE_TEST here.
> > >
> > > IOMMU_IO_PGTABLE_LPAE and IOMMU_IO_PGTABLE_ARMV7S are
> > > selected by other symbols that can be enabled when compile-testing, so
> > > the tests can still be enabled in those cases, too
> >
> > Sure, but when you want to compile-test a thing, what would you rather
> > do: enable the thing, or go hunting to find some other thing that
> > happens to select the thing you actually want, then potentially have to
> > figure out *that* thing's dependencies, and so on?
>
> Agreed.
>
> > Coverage isn't solely about whether it's technically possible to ever
> > reach somewhere at all, it's just as much about how easily and/or often
> > you can get there in practice. I don't see who benefits from making
> > COMPILE_TEST harder to use :/
>
> So perhaps the visibility of IOMMU_IO_PGTABLE_LPAE and
> IOMMU_IO_PGTABLE_ARMV7S should depend on COMPILE_TEST?
> Normal users would still get it through select when needed.

As I say those still offer functionality beyond compile-testing, but now 
you've got me suspecting that it's already suboptimal that one has to 
enable the format to make the self-test option appear... Perhaps what we 
want is a separate master option to enable io-pgtable self-tests in 
general, then rejig the rest around that.

Of course the self-tests would be even more useful if the harness was at 
the level of the core io-pgtable API so it could cover new formats 
automatically as long as they provide the configuration parameters, but 
that's a separate matter for someone with sufficient free time and 
enthusiasm :)

Cheers,
Robin.