Re: [PATCH] drm/panfrost: fix GENERIC_ATOMIC64 dependency

[Robin Murphy]

On 2023-01-18 11:09, Steven Price wrote:
> On 17/01/2023 16:44, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > On ARMv5 and earlier, a randconfig build can still run into
> >
> > WARNING: unmet direct dependencies detected for IOMMU_IO_PGTABLE_LPAE
> >    Depends on [n]: IOMMU_SUPPORT [=y] && (ARM [=y] || ARM64 || COMPILE_TEST [=y]) && !GENERIC_ATOMIC64 [=y]
> >    Selected by [y]:
> >    - DRM_PANFROST [=y] && HAS_IOMEM [=y] && DRM [=y] && (ARM [=y] || ARM64 || COMPILE_TEST [=y] && !GENERIC_ATOMIC64 [=y]) && MMU [=y]
> >
> > Rework the dependencies to always require a working cmpxchg64.
> >
> > Fixes: db594ba3fcf9 ("drm/panfrost: depend on !GENERIC_ATOMIC64 when using COMPILE_TEST")
>
> Looking at db594ba3fcf9 - it states:
>
> >      Since panfrost has a 'select' on IOMMU_IO_PGTABLE_LPAE we must depend on
> >      the same set of flags. Otherwise IOMMU_IO_PGTABLE_LPAE will be forced on
> >      even though it cannot build (no support for cmpxchg64).
>
> And at the time the dependencies on IOMMU_IO_PGTABLE_LPAE were exactly
> these.
>
> However d286a58bc8f4 ("iommu: Tidy up io-pgtable dependencies")
> (currently in the iommu tree) changed the depends to split the
> !GENERIC_ATOMIC64 out. So we could argue that really that's the commit
> that should be blamed in the fixes line.

Oh bum... indeed this is entirely my fault for forgetting about our one 
"foreign" io-pgtable user in that commit, sorry about that.

> However there's no harm in this being backported further than it
> strictly needs to be, and it's clearly better having the
> !GENERIC_ATOMIC64 split out. So I'll merge this to drm-misc-fixes.

Thanks both!

Robin.

> Reviewed-by: Steven Price <steven.price@xxxxxxx>
>
> Thanks!
>
> Steve
>
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> >   drivers/gpu/drm/panfrost/Kconfig | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/panfrost/Kconfig b/drivers/gpu/drm/panfrost/Kconfig
> > index 079600328be1..e6403a9d66ad 100644
> > --- a/drivers/gpu/drm/panfrost/Kconfig
> > +++ b/drivers/gpu/drm/panfrost/Kconfig
> > @@ -3,7 +3,8 @@
> >   config DRM_PANFROST
> >   	tristate "Panfrost (DRM support for ARM Mali Midgard/Bifrost GPUs)"
> >   	depends on DRM
> > -	depends on ARM || ARM64 || (COMPILE_TEST && !GENERIC_ATOMIC64)
> > +	depends on ARM || ARM64 || COMPILE_TEST
> > +	depends on !GENERIC_ATOMIC64    # for IOMMU_IO_PGTABLE_LPAE
> >   	depends on MMU
> >   	select DRM_SCHED
> >   	select IOMMU_SUPPORT