Linux Virtualization - Oct 2016 - [PATCH v9 17/19] drm/virtio: kconfig: Fix recursive dependency issue.

Hi Bjorn,

On 27 September 2016 at 18:01, Bjorn Andersson
<bjorn.andersson at linaro.org> wrote:
> On Wed 21 Sep 05:09 PDT 2016, Emil Velikov wrote:
>
>> On 20 September 2016 at 09:32, Peter Griffin <peter.griffin at
linaro.org> wrote:
>> > Hi Emil,
>> >
>> > On Tue, 20 Sep 2016, Emil Velikov wrote:
>> >
>> >> On 5 September 2016 at 14:16, Peter Griffin <peter.griffin
at linaro.org> wrote:
>> >> > ST_SLIM_REMOTEPROC must select REMOTEPROC, which exposes
the following
>> >> > recursive dependency.
>> >
>> >
>> >> >
>> >> From a humble skim through remoteproc, drm and a few other
subsystems
>> >> I think the above is wrong. All the drivers (outside of
remoteproc),
>> >> that I've seen, depend on the core component, they
don't select it.
>> >
>> > I will let Bjorn comment on the remoteproc subsystem Kconfig
design, and
>> > why it is like it is.
>> >
>> > For this particular SLIM_RPROC I have added it to Kconfig in
keeping with all
>> > the other drivers in the remoteproc subsystem which has exposed
this recursive
>> > dependency issue.
>> >
>> > For this particular kconfig symbol a quick grep reveals more
drivers in
>> > the kernel using 'select', than 'depend on'
>> >
>> > git grep "select VIRTIO" | wc -l
>> > 14
>> >
>> > git grep "depends on VIRTIO" | wc -l
>> > 10
>> >
>> Might be worth taking a closer look into these at some point.
>>
>
> The general idea here is that VIRTIO provides the "framework" and
as
> such drivers implementing VIRTIO do select and drivers using virtio use
> depends.
>
> This is found in several places around the kernel.
>
>> >
>> >> Furthermore most places explicitly hide the drivers from the
menu if
>> >> the core component isn't enabled.
>> >
>> > Remoteproc subsystem takes a different approach, the core code is
only enabled
>> > if a driver which relies on it is enabled. This IMHO makes sense,
as
>> > remoteproc is not widely used (only a few particular ARM
SoC's).
>> >
>> > It is true that for subsystems which rely on the core component
being
>> > explicitly enabled, they often tend to hide drivers which depend
on it
>> > from the menu unless it is. This also makes sense.
>> >
>> >>
>> >> Is there something that requires such a different/unusual
behaviour in
>> >> remoteproc ?
>> >>
>
> There's nothing unusual in remoteproc that forces us to stay with this
> model; however the parts related to the REMOTEPROC config is useless by
> themselves.
>
I'm afraid that the "supporting" arguments you're using are
generic
and not specific to remoteproc. Although as Jani mentioned and pointed
to the documentation, remoteproc is {mis,ab}using 'select' leading to
issues elsewhere.

In the long term we might want to switch to 'select' and attribute
kconfig like Jani suggested.  But in the short term we want to avoid
select-ing things just for our "convenience".

Thanks
Emil