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

Nick Desaulniers
2023-05-24T18:56:36Z

On Wed, May 24, 2023 at 11:41 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> 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>

Ah then I guess my link tag should have been

Closes: https://lore.kernel.org/all/20230523125116.1669057-1-trix@redhat.com/

I hope the author of
commit 44c31888098a ("checkpatch: allow Closes tags with links")
has coordinated with the maintainer of b4, so that b4 recognizes Closes tags.
b4 v0.12.2 does not pick up Closes tags.
--
Thanks,
~Nick Desaulniers