Re: [PATCH] drm/i915: Fix clang -Wimplicit-fallthrough in intel_async_flip_check_hw()

[Nathan Chancellor <nathan@kernel.org>]

On Wed, May 24, 2023 at 11:32:32AM -0700, Nick Desaulniers wrote:
> On Wed, May 24, 2023 at 8:38 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > Clang warns:
> >
> >   drivers/gpu/drm/i915/display/intel_display.c:6012:3: error: unannotated fall-through between switch labels [-Werror,-Wimplicit-fallthrough]
> >                   case I915_FORMAT_MOD_X_TILED:
> >                   ^
> >   drivers/gpu/drm/i915/display/intel_display.c:6012:3: note: insert 'break;' to avoid fall-through
> >                   case I915_FORMAT_MOD_X_TILED:
> >                   ^
> >                   break;
> >   1 error generated.
> >
> > Clang is a little more pedantic than GCC, which does not warn when
> > falling through to a case that is just break or return. Clang's version
> > is more in line with the kernel's own stance in deprecated.rst, which
> > states that all switch/case blocks must end in either break,
> > fallthrough, continue, goto, or return. Add the missing break to silence
> > the warning.
> >
> > Fixes: 937859485aef ("drm/i915: Support Async Flip on Linear buffers")
> > Reported-by: kernel test robot <lkp@intel.com>
> > Closes: https://lore.kernel.org/202305241902.UvHtMoxa-lkp@intel.com/
> > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> > Closes: https://lore.kernel.org/CA+G9fYv68V3ewK0Qj-syQj7qX-hQr0H1MFL=QFNuDoE_J2Zu-g@mail.gmail.com/
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> 
> Thanks for the patch! I've never seen the closes tag before, that's
> new to me. Can you tell me more about it?

It is new to me (at least in the context of the kernel) as well. I only
used it over Link: because checkpatch.pl told me to:

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#26:
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#27:
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

It was Link: for a bit but commit 44c31888098a ("checkpatch: allow
Closes tags with links") changed it to Closes:. Looks odd to me but
whatever the linter says I suppose.

Thanks for the review!

Cheers,
Nathan

> A few more tags
> 
> Reported-by: Tom Rix <trix@redhat.com>
> Link: https://lore.kernel.org/all/20230523125116.1669057-1-trix@redhat.com/
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> 
> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_display.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > index 0490c6412ab5..6d49e0ab3e85 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -6008,6 +6008,7 @@ static int intel_async_flip_check_hw(struct intel_atomic_state *state, struct in
> >                                             plane->base.base.id, plane->base.name);
> >                                 return -EINVAL;
> >                         }
> > +                       break;
> >
> >                 case I915_FORMAT_MOD_X_TILED:
> >                 case I915_FORMAT_MOD_Y_TILED:
> >
> > ---
> > base-commit: 9a2cb1b31c040e2f1b313e2f7921f0f5e6b66d82
> > change-id: 20230524-intel_async_flip_check_hw-implicit-fallthrough-c4c40b03802f
> >
> > Best regards,
> > --
> > Nathan Chancellor <nathan@kernel.org>
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers