linux-kernel - Re: [PATCH] drm: atomic helper: fix W=1 warnings

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Message-ID: <20191004122747.GT1208@intel.com>
Date:   Fri, 4 Oct 2019 15:27:47 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Benjamin Gaignard <benjamin.gaignard@...aro.org>
Cc:     Benjamin Gaignard <benjamin.gaignard@...com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm: atomic helper: fix W=1 warnings

On Fri, Oct 04, 2019 at 12:48:02PM +0200, Benjamin Gaignard wrote:
> Le jeu. 3 oct. 2019 à 17:46, Ville Syrjälä
> <ville.syrjala@...ux.intel.com> a écrit :
> >
> > On Thu, Oct 03, 2019 at 05:37:15PM +0200, Benjamin Gaignard wrote:
> > > Le jeu. 3 oct. 2019 à 17:05, Ville Syrjälä
> > > <ville.syrjala@...ux.intel.com> a écrit :
> > > >
> > > > On Thu, Oct 03, 2019 at 04:46:54PM +0200, Benjamin Gaignard wrote:
> > > > > Le jeu. 3 oct. 2019 à 16:27, Ville Syrjälä
> > > > > <ville.syrjala@...ux.intel.com> a écrit :
> > > > > >
> > > > > > On Mon, Sep 09, 2019 at 03:52:05PM +0200, Benjamin Gaignard wrote:
> > > > > > > Fix warnings with W=1.
> > > > > > > Few for_each macro set variables that are never used later.
> > > > > > > Prevent warning by marking these variables as __maybe_unused.
> > > > > > >
> > > > > > > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
> > > > > > > ---
> > > > > > >  drivers/gpu/drm/drm_atomic_helper.c | 36 ++++++++++++++++++------------------
> > > > > > >  1 file changed, 18 insertions(+), 18 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > > > > > > index aa16ea17ff9b..b69d17b0b9bd 100644
> > > > > > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > > > > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > > > > > @@ -262,7 +262,7 @@ steal_encoder(struct drm_atomic_state *state,
> > > > > > >             struct drm_encoder *encoder)
> > > > > > >  {
> > > > > > >       struct drm_crtc_state *crtc_state;
> > > > > > > -     struct drm_connector *connector;
> > > > > > > +     struct drm_connector __maybe_unused *connector;
> > > > > >
> > > > > > Rather ugly. IMO would be nicer if we could hide something inside
> > > > > > the iterator macros to suppress the warning.
> > > > >
> > > > > Ok but how ?
> > > > > connector is assigned in the macros but not used later and we can't
> > > > > set "__maybe_unused"
> > > > > in the macro.
> > > > > Does another keyword exist for that ?
> > > >
> > > > Stick a (void)(connector) into the macro?
> > >
> > > That could work but it will look strange inside the macro.
> > >
> > > >
> > > > Another (arguably cleaner) idea would be to remove the connector/crtc/plane
> > > > argument from the iterators entirely since it's redundant, and instead just
> > > > extract it from the appropriate new/old state as needed.
> > > >
> > > > We could then also add a for_each_connector_in_state()/etc. which omit
> > > > s the state arguments and just has the connector argument, for cases where
> > > > you don't care about the states when iterating.
> > >
> > > That may lead to get a macro for each possible combination of used variables.
> >
> > We already have new/old/oldnew, so would "just" add one more.
> 
> Not just one, it will be one each new/old/oldnew macro to be able to distinguish
> when connector is used or not.

What I'm suggesting is this:
for_each_connector_in_state(state, connector, i)
for_each_old_connector_in_state(state, old_conn_state, i)
for_each_new_connector_in_state(state, new_conn_state, i)
for_each_oldnew_connector_in_state(state, old_conn_state, new_conn_state, i)

So only four in total for each object type, instead of the current
three.

-- 
Ville Syrjälä
Intel