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

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Message-ID: <11447519.fzG14qnjOE@e123338-lin>
Date:   Tue, 26 Nov 2019 15:55:09 +0000
From:   Mihail Atanassov <Mihail.Atanassov@....com>
To:     Daniel Vetter <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
CC:     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()

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.

> 
> > ---
> >  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.

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