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

From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <nathan@kernel.org>
Cc: tvrtko.ursulin@linux.intel.com, llvm@lists.linux.dev,
	kernel test robot <lkp@intel.com>,
	trix@redhat.com, intel-gfx@lists.freedesktop.org,
	patches@lists.linux.dev, dri-devel@lists.freedesktop.org,
	rodrigo.vivi@intel.com,
	Naresh Kamboju <naresh.kamboju@linaro.org>
Subject: Re: [PATCH] drm/i915: Fix clang -Wimplicit-fallthrough in intel_async_flip_check_hw()
Date: Wed, 24 May 2023 11:32:32 -0700	[thread overview]
Message-ID: <CAKwvOd=jZJouuNMd3Rvc--goA0EXPHcf6cHXUA6W1kXJg2ay2w@mail.gmail.com> (raw)
In-Reply-To: <20230524-intel_async_flip_check_hw-implicit-fallthrough-v1-1-83de89e376a1@kernel.org>

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?

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