linux-kernel - Re: [PATCH 01/30] drm: Introduce drm_bridge

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Message-ID: <CAKMK7uG2T9hPCsQ6yLekGoz5qA2-ePa2_MmsmQRBH5je+7Kaow@mail.gmail.com>
Date:   Tue, 26 Nov 2019 18:04:24 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Mihail Atanassov <Mihail.Atanassov@....com>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        nd <nd@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/30] drm: Introduce drm_bridge_init()

On Tue, Nov 26, 2019 at 4:55 PM Mihail Atanassov
<Mihail.Atanassov@....com> wrote:
>
> Hi Daniel,
>
> Thanks for the quick review.
>
> On Tuesday, 26 November 2019 14:26:10 GMT Daniel Vetter wrote:
> > On Tue, Nov 26, 2019 at 01:15:59PM +0000, Mihail Atanassov wrote:
> > > A simple convenience function to initialize the struct drm_bridge.
> > >
> > > Signed-off-by: Mihail Atanassov <mihail.atanassov@....com>
> >
> > The commit message here leaves figuring out why we need this to the
> > reader. Reading ahead the reasons seems to be to roll out bridge->dev
> > setting for everyone, so that we can set the device_link. Please explain
> > that in the commit message so the patch is properly motivated.
>
> Ack, but with one caveat: bridge->dev is the struct drm_device that is
> the bridge client, we need to add a bridge->device (patch 29 in this
> series) which is the struct device that will manage the bridge lifetime.

Ah yes, ->dev is for drm_bridge_attach.

> >
> > > ---
> > >  drivers/gpu/drm/drm_bridge.c | 29 +++++++++++++++++++++++++++++
> > >  include/drm/drm_bridge.h     |  4 ++++
> > >  2 files changed, 33 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > > index cba537c99e43..cbe680aa6eac 100644
> > > --- a/drivers/gpu/drm/drm_bridge.c
> > > +++ b/drivers/gpu/drm/drm_bridge.c
> > > @@ -89,6 +89,35 @@ void drm_bridge_remove(struct drm_bridge *bridge)
> > >  }
> > >  EXPORT_SYMBOL(drm_bridge_remove);
> > >
> > > +/**
> > > + * drm_bridge_init - initialise a drm_bridge structure
> > > + *
> > > + * @bridge: bridge control structure
> > > + * @funcs: control functions
> > > + * @dev: device
> > > + * @timings: timing specification for the bridge; optional (may be NULL)
> > > + * @driver_private: pointer to the bridge driver internal context (may be NULL)
> >
> > Please also sprinkle some links to this new function to relevant places,
> > I'd add at least:
> >
> > "Drivers should call drm_bridge_init() first." to the kerneldoc for
> > drm_bridge_add. drm_bridge_add should also mention drm_bridge_remove as
> > the undo function.
> >
> > And perhaps a longer paragraph to &struct drm_bridge:
> >
> > "Bridge drivers should call drm_bridge_init() to initialized a bridge
> > driver, and then register it with drm_bridge_add().
> >
> > "Users of bridges link a bridge driver into their overall display output
> > pipeline by calling drm_bridge_attach()."
>
> Will do.
>
> >
> > > + */
> > > +void drm_bridge_init(struct drm_bridge *bridge, struct device *dev,
> > > +                const struct drm_bridge_funcs *funcs,
> > > +                const struct drm_bridge_timings *timings,
> > > +                void *driver_private)
> > > +{
> > > +   WARN_ON(!funcs);
> > > +
> > > +   bridge->dev = NULL;
> >
> > Given that the goal here is to get bridge->dev set up, why not
> >
> >       WARN_ON(!dev);
> >       bridge->dev = dev;
>
> See above struct device vs struct drm_device. I add a
>
>         bridge->device = dev;
>
> in patch 29, which takes care of that. I skipped the warn since
> there's a dereference of dev, but I now realized it's behind CONFIG_OF,
> so I'll add it in for v2.

Ok, sounds good. Having the WARN_ON in patch 1 should also help making
sure all the conversion patches dtrt (and any future users).
-Daniel

> Yes, 'device' isn't the best of names, but I took Russell's patch
> almost as-is, I didn't have any better ideas for bikeshedding.
>
> >
> > That should help us to really move forward with all this.
> > -Daniel
> >
> > > +   bridge->encoder = NULL;
> > > +   bridge->next = NULL;
> > > +
> > > +#ifdef CONFIG_OF
> > > +   bridge->of_node = dev->of_node;
> > > +#endif
> > > +   bridge->timings = timings;
> > > +   bridge->funcs = funcs;
> > > +   bridge->driver_private = driver_private;
> > > +}
> > > +EXPORT_SYMBOL(drm_bridge_init);
> > > +
> > >  /**
> > >   * drm_bridge_attach - attach the bridge to an encoder's chain
> > >   *
> > > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> > > index c0a2286a81e9..d6d9d5301551 100644
> > > --- a/include/drm/drm_bridge.h
> > > +++ b/include/drm/drm_bridge.h
> > > @@ -402,6 +402,10 @@ struct drm_bridge {
> > >
> > >  void drm_bridge_add(struct drm_bridge *bridge);
> > >  void drm_bridge_remove(struct drm_bridge *bridge);
> > > +void drm_bridge_init(struct drm_bridge *bridge, struct device *dev,
> > > +                const struct drm_bridge_funcs *funcs,
> > > +                const struct drm_bridge_timings *timings,
> > > +                void *driver_private);
> > >  struct drm_bridge *of_drm_find_bridge(struct device_node *np);
> > >  int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
> > >                   struct drm_bridge *previous);
> >
> >
>
>
> --
> Mihail
>
>
>


--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch