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

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Date:   Wed, 19 May 2021 21:41:27 -0400
From:   Stephen Boyd <swboyd@...omium.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH 0/7] component: Make into an aggregate bus

Quoting Saravana Kannan (2021-05-19 18:27:50)
> On Wed, May 19, 2021 at 5:25 PM Stephen Boyd <swboyd@...omium.org> 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@...ll.ch>
> > Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> > Cc: Rob Clark <robdclark@...il.com>
> > Cc: Russell King <rmk+kernel@....linux.org.uk>
> > Cc: Saravana Kannan <saravanak@...gle.com>
> >
> > [1] https://lore.kernel.org/r/20210508074118.1621729-1-swboyd@chromium.org
> >
>
> 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.