[PATCH] drm/amdgpu: select ARCH_HAS_HMM and ZONE_DEVICE option

[Jerome Glisse]

On Thu, Feb 21, 2019 at 12:17:33AM +0000, Kuehling, Felix wrote:
> On 2019-02-20 6:34 p.m., Jerome Glisse wrote:
> > On Wed, Feb 20, 2019 at 10:39:49PM +0000, Kuehling, Felix wrote:
> >> On 2019-02-20 5:12 p.m., Jerome Glisse wrote:
> >>> On Wed, Feb 20, 2019 at 07:18:17PM +0000, Kuehling, Felix wrote:
> >>>> [+Jerome]
> >>>>
> >>>> Why to we need ZONE_DEVICE. I didn't think this was needed for mirroring
> >>>> CPU page tables to device page tables.
> >>>>
> >>>> ARCH_HAS_HMM depends on (X86_64 || PPC64). Do we have some alternative
> >>>> for ARM support?
> >>>>
> >>>> Also, the name ARCH_HAS_HMM looks like it's meant to be selected by the
> >>>> CPU architecture rather than any driver. Jerome, do you have any advice?
> >>> This patch is wrong you need to depend on ARCH_HAS_HMM and
> >> Who selects ARCH_HAS_HMM? Currently I don't see this selected anywhere.
> >> So any config option that depends on it will be invisible in menuconfig.
> >> Do we need ARCH_HAS_HMM somewhere in the arch/x86/Kconfig and
> >> arch/powerpc/Kconfig?
> >>
> >> Also, ARCH_HAS_HMM does not currently support ARM. Does that mean we
> >> can't have ARM support in AMDGPU if we start using HMM?
> > ARCH_HAS_HMM is defined by architecture that support HMM. So par x86
> > and PPC. It should not be hard to add it to ARM (i can not remember if
> > ARM has DAX yet or not, if ARM does not have DAX then you need to add
> > that first).
> 
> Not having ARM support is a bummer. I just enabled KFD on ARM a few 
> weeks ago. Now depending on HMM makes KFD unusable on ARM. [+Mark FYI] I 
> hope this is only a temporary setback.

It should not be hard to add in fact all it might need is a Kconfig
patch. I have no easy access to ARM with PCIE so i have not tackle
this yet.

> 
> 
> >> Finally, ARCH_HAS_HMM has a bunch of dependencies. If they are not met,
> >> I guess it can't be enabled. Should those be "select"s instead?
> > No they should not be selected, people configuring their system need
> > to have the freedom of doing so. All those option are selected in all
> > the big distribution.
> As far as I can tell, the arch/x86/Kconfig doesn't select ARCH_HAS_HMM. 
> Its default is "y", so it should be enabled on anything that meets the 
> dependencies. But ZONE_DEVICE was not enabled by default. I think that's 
> what broke our kernel configs.
> 
> We'll fix our own kernel configs to enable ZONE_DEVICE and ARCH_HAS_HMM 
> to get our internal builds to work again.

You seem to be doing weird thing with your kconfig ...

> 
> I suspect other users with their own kernel configs will stumble over 
> this and wonder why KFD and userptr support are disabled in their builds.

Patch to improve kconfig are welcome but they should not force select
thing. Configuration is there to give user freedom to select fewature
they want to give up.

Maybe following would help:
ARCH_HAS_HMM
-	bool
-	default y
+	def_bool y

Cheers,
Jérôme