Re: [PATCH] drm/sun4i: Clear encoder->bridge if a bridge is not found

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Aug 31, 2016 at 05:40:02PM +0200, Maxime Ripard wrote:
> On Tue, Aug 30, 2016 at 11:51:26PM +0800, Chen-Yu Tsai wrote:
> > On Tue, Aug 30, 2016 at 8:56 PM, Maxime Ripard
> > <maxime.ripard@free-electrons.com> wrote:
> > > Hi,
> > >
> > > On Tue, Aug 30, 2016 at 08:22:23PM +0800, Chen-Yu Tsai wrote:
> > >> The KMS helpers (drm_atomic_helper_check_modeset/mode_fixup) pass
> > >> encoder->bridge directly to drm_bridge_mode_fixup, which expects a
> > >> valid pointer, or NULL (in which case it just returns).
> > >>
> > >> Clear encoder->bridge if a bridge is not found, instead of keeping
> > >> the ERR_PTR value.
> > >>
> > >> Since other drm_bridge functions also follow this pattern of checking
> > >> for a non-NULL pointer, we can drop the ifs around the calls and just
> > >> pass the pointer directly.
> > >>
> > >> Fixes: 894f5a9f4b4a ("drm/sun4i: Add bridge support")
> > >> Signed-off-by: Chen-Yu Tsai <wens@csie.org>
> > >> ---
> > >>  drivers/gpu/drm/sun4i/sun4i_rgb.c | 11 ++++++-----
> > >>  1 file changed, 6 insertions(+), 5 deletions(-)
> > >>
> > >> diff --git a/drivers/gpu/drm/sun4i/sun4i_rgb.c b/drivers/gpu/drm/sun4i/sun4i_rgb.c
> > >> index d4e52522ec53..ee0795152a33 100644
> > >> --- a/drivers/gpu/drm/sun4i/sun4i_rgb.c
> > >> +++ b/drivers/gpu/drm/sun4i/sun4i_rgb.c
> > >> @@ -154,8 +154,7 @@ static void sun4i_rgb_encoder_enable(struct drm_encoder *encoder)
> > >>       if (!IS_ERR(tcon->panel))
> > >>               drm_panel_enable(tcon->panel);
> > >>
> > >> -     if (!IS_ERR(encoder->bridge))
> > >> -             drm_bridge_enable(encoder->bridge);
> > >> +     drm_bridge_enable(encoder->bridge);
> > >>
> > >>       sun4i_tcon_channel_enable(tcon, 0);
> > >>  }
> > >> @@ -170,8 +169,7 @@ static void sun4i_rgb_encoder_disable(struct drm_encoder *encoder)
> > >>
> > >>       sun4i_tcon_channel_disable(tcon, 0);
> > >>
> > >> -     if (!IS_ERR(encoder->bridge))
> > >> -             drm_bridge_disable(encoder->bridge);
> > >> +     drm_bridge_disable(encoder->bridge);
> > >
> > > I'd rather keep those changes, it makes it obvious that it's something
> > > optionnal, that can be set to NULL.
> > 
> > OK.
> > 
> > >>       if (!IS_ERR(tcon->panel))
> > >>               drm_panel_disable(tcon->panel);
> > >> @@ -230,6 +228,9 @@ int sun4i_rgb_init(struct drm_device *drm)
> > >>               return 0;
> > >>       }
> > >>
> > >> +     if (IS_ERR(encoder->bridge))
> > >> +             encoder->bridge = NULL;
> > >> +
> > >
> > > And that could be the else condition of the if statement below.
> > 
> > That would be a bit confusing, changing it after calling drm_encoder_init.
> > The code says it ok to do though.
> 
> The magic really happens only after the encoder has been attached to
> something, so it's really safe.

s/attached/registered using drm_dev_register(). Which should
happen _way_ later for all drivers which have gotten rid of their ->load
callback and implemented the recommend driver load sequence.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch