Re: [PATCH 2/2] nouveau: fix dependencies for DEVICE_PRIVATE

[Arnd Bergmann]

On Fri, May 8, 2020 at 9:04 PM Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote:
>
> On Fri, May 08, 2020 at 05:05:03PM +0200, Arnd Bergmann wrote:
> > On Fri, May 8, 2020 at 5:00 PM Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote:
> > >
> > > On Fri, May 08, 2020 at 04:40:09PM +0200, Arnd Bergmann wrote:
> > > > CONFIG_DEVICE_PRIVATE cannot be selected in configurations
> > > > without ZONE_DEVICE:
> > >
> > > It is kind of unfortunate to lift dependencies from DEVICE_PRIVATE
> > > into the users, is this really how kconfig is supposed to work or is
> > > something else wrong here?
> >
> > Usually the problem is trying to use 'select' for something that can
> > be done with 'depends on'. I have actually no idea what
> > CONFIG_DEVICE_PRIVATE does, as it lacks a help text
> > and is a rather generic term.
>
> It is a sub mode of ZONE_DEVICE, ie DEVICE_PRIVATE turns on a certain
> kind of ZONE_DEVICE page.
>
> Both ZONE_DEVICE and DEVICE_PRIVATE are APIs families drivers use,
> there is no reason for a user to select either of these directly.

Ok, then how about making ZONE_DEVICE a hidden symbol and adding
something like

config ZONE_DEVICE_POSSIBLE
        def_bool y
        depends on MEMORY_HOTPLUG
        depends on MEMORY_HOTREMOVE
        depends on SPARSEMEM_VMEMMAP
        depends on ARCH_HAS_PTE_DEVMAP

then drivers that want it can do

config FOO
        tristate "user visible option"
        depends on ZONE_DEVICE_POSSIBLE
        select ZONE_DEVICE

      Arnd