linux-kernel - Re: [Intel-gfx] [PATCH RESEND] drm/i915: Fix pipe/transcoder enum mismatches

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Message-ID: <20170713122454.jmhqlxl4z76qdf6g@phenom.ffwll.local>
Date:   Thu, 13 Jul 2017 14:24:54 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Stéphane Marchesin <marcheu@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Michael Davidson <md@...gle.com>,
        Grant Grundler <grundler@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [Intel-gfx] [PATCH RESEND] drm/i915: Fix pipe/transcoder enum
 mismatches

On Thu, Jul 13, 2017 at 01:13:51PM +0300, Ville Syrjälä wrote:
> On Wed, Jul 12, 2017 at 07:28:14PM -0700, Stéphane Marchesin wrote:
> > On Fri, May 5, 2017 at 10:40 AM, Ville Syrjälä
> > <ville.syrjala@...ux.intel.com> wrote:
> > >
> > > On Fri, May 05, 2017 at 10:26:36AM -0700, Matthias Kaehlcke wrote:
> > > > El Thu, Apr 20, 2017 at 02:56:05PM -0700 Matthias Kaehlcke ha dit:
> > > >
> > > > > In several instances the driver passes an 'enum pipe' value to a
> > > > > function expecting an 'enum transcoder' and viceversa. Since PIPE_x and
> > > > > TRANSCODER_x have the same values this doesn't cause functional
> > > > > problems. Still it is incorrect and causes clang to generate warnings
> > > > > like this:
> > > > >
> > > > > drivers/gpu/drm/i915/intel_display.c:1844:34: warning: implicit
> > > > >   conversion from enumeration type 'enum transcoder' to different
> > > > >   enumeration type 'enum pipe' [-Wenum-conversion]
> > > > >     assert_fdi_rx_enabled(dev_priv, TRANSCODER_A);
> > > > >
> > > > > Change the code to pass values of the type expected by the callee.
> > > > >
> > > > > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > > > > ---
> > > > >  drivers/gpu/drm/i915/intel_display.c | 4 ++--
> > > > >  drivers/gpu/drm/i915/intel_dp.c      | 6 ++++--
> > > > >  drivers/gpu/drm/i915/intel_hdmi.c    | 6 ++++--
> > > > >  drivers/gpu/drm/i915/intel_sdvo.c    | 6 ++++--
> > > > >  4 files changed, 14 insertions(+), 8 deletions(-)
> > > >
> > > > Ping, any comments on this patch?
> > >
> > > I'm not convinced the patch is making things any better really. To
> > > fix this really properly, I think we'd need to introduce a new enum
> > > pch_transcoder and thus avoid the confusion of which type of
> > > transcoder we're talking about. Currently most places expect an
> > > enum pipe when dealing with PCH transcoders, and enum transcoder
> > > when dealing with CPU transcoders. But there are some exceptions
> > > of course.
> > 
> > 
> > I don't follow -- these functions take an enum transcoder; what's
> > wrong about passing what they expect? It seems like what you are
> > asking for has nothing to do with the warning here...
> 
> There's a warning? I don't get any.
> 
> Anyways, I just don't see much point in blindly changing the types
> because it doesn't actually solve the underlying confusion for human
> readers. It might even make it worse, not sure.

Yeah the current patch just makes it worse. Either enum pch_transcoder, or
the enum pipe changes I suggested somewhere else. Blindly fixing type
mismatches without actually fixing the underlying confusion isn't really
useful work. And at least the switch to enum pipe for pch won't be (much)
bigger.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch