Re: [PATCH 0/7] component: Make into an aggregate bus

[Daniel Vetter]

On Wed, May 19, 2021 at 09:41:27PM -0400, Stephen Boyd wrote:
> Quoting Saravana Kannan (2021-05-19 18:27:50)
> > On Wed, May 19, 2021 at 5:25 PM Stephen Boyd <swboyd@xxxxxxxxxxxx> wrote:
> > >
> > > This series is from discussion we had on reordering the device lists for
> > > drm shutdown paths[1]. I've introduced an 'aggregate' bus that we put
> > > the aggregate device onto and then we probe the device once all the
> > > components are probed and call component_add(). The probe/remove hooks
> > > are where the bind/unbind calls go, and then a shutdown hook is added
> > > that can be used to shutdown the drm display pipeline at the right time.
> > >
> > > This works for me on my sc7180 board, but I'm currently struggling with
> > > the last patch where we migrate the msm driver. It runs into a runtime
> > > PM problem where the parent device isn't runtime PM enabled yet. I'm
> > > still trying to figure out a clean solution there. Moving runtime PM
> > > around breaks boot and I think that's because the power domain is off.
> > >
> > > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > > Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> > > Cc: Rob Clark <robdclark@xxxxxxxxx>
> > > Cc: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> > > Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
> > >
> > > [1] https://lore.kernel.org/r/20210508074118.1621729-1-swboyd@xxxxxxxxxxxx
> > >
> >
> > I skimmed through the series and in general the idea is good, but I'm
> > not sure why each component user needs to be converted/"modern" before
> > it can make use of the benefits of this series. Why not just have
> > wrapper functions around the component ops that the new aggregate bus
> > driver can just call? That'll give all the existing component users
> > the new ability to use the new ops without having to have two
> > versions.
> 
> The existing users can only have one or the other. Either use the ops
> structure or use the struct aggregate_driver. What benefits of this
> series are they not gaining?
> 
> > That'll also allow us to do other improvements (I have some
> > in mind) that'll apply to all the component users instead of only the
> > converted ones.
> 
> What do you have in mind? I didn't want to convert drivers over to the
> new way of doing things without making them consciously change their
> code. Otherwise I worry it will break things in random, subtle ways. The
> last patch, as I mentioned above in the cover, causes warnings because
> the display driver is enabling runtime PM in an odd spot as part of the
> bind callback of the aggregate/master. That should move out of there and
> into the msm_pdev driver that registers the aggregate from what I can
> tell.

Hm yeah that's annoying. Another thing to check is that there's no locking
issues with lockdep enabled. But there's plenty of other places that
register/bind drivers within other drivers, so it should all work.

I think this is a good reason why more drivers should be converted (in
separate patches) so that we get a lot more testing and can find bugs in
the design.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch