Nouveau - May 2020 - [PATCH 2/2] nouveau: fix dependencies for DEVICE_PRIVATE

On Fri, May 8, 2020 at 5:00 PM Jason Gunthorpe <jgg at mellanox.com>
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.

Would it be possible to decouple DEVICE_PRIVATE from ZONE_DEVICE?
It sounds like the first is related to the device model, while
the second is for memory management, so maybe the dependency
is not necessary.

       Arnd

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 at mellanox.com>
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.

Jason

On Fri, May 8, 2020 at 9:04 PM Jason Gunthorpe <jgg at mellanox.com>
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 at
mellanox.com> 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