linux-kernel - Re: [PATCH RFC] drm/radeon/ci add comment to document intentionally unreachable code

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Message-ID: <CADnq5_Np3QApNKm7ZUFyRu2w72YirFadgCJ_uS4dYKC8UbwK5A@mail.gmail.com>
Date:	Wed, 27 Jul 2016 16:33:23 -0400
From:	Alex Deucher <alexdeucher@...il.com>
To:	Nicholas Mc Guire <hofrat@...dl.org>
Cc:	Alex Deucher <alexander.deucher@....com>,
	Christian Koenig <christian.koenig@....com>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] drm/radeon/ci add comment to document intentionally
 unreachable code

On Tue, Jul 19, 2016 at 3:54 PM, Nicholas Mc Guire <hofrat@...dl.org> wrote:
>  commit d967be9b80a5 ("drm/radeon/ci: disable needless sclk changes")
>  introduces an unreachable if(C != C) conditional code section
>  flagged by coccinelle script bad_conditional.cocci:
>
>  Add a comment to make it clear that this is intentional.
>
>  Fixes: d967be9b80a5 ("drm/radeon/ci: disable needless sclk changes")
>
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>

Applied.  thanks.

Alex

> ---
>         ./drivers/gpu/drm/radeon/ci_dpm.c:3847 bad/useless conditional
> <snip>
> 3845     } else {
> 3846          /* XXX check display min clock requirements */
> 3847          if (CISLAND_MINIMUM_ENGINE_CLOCK !=
> CISLAND_MINIMUM_ENGINE_CLOCK)
> 3848               pi->need_update_smu7_dpm_table |= DPMTABLE_UPDATE_SCLK;
> 3849     }
> <snip>
>
>  which is unreachable given the condition - as this seems to be an
>  intentional disabling of that code section as stated in the commit
>  message of d967be9b80a5 ("drm/radeon/ci: disable needless sclk changes")
>  that introduced that change it should be at least commented
>
>   in drivers/gpu/drm/amd/amdgpu/ci_dpm.c at line 3988
> 3986    } else {
> 3987        /* XXX check display min clock requirements */
> 3988        if (CISLAND_MINIMUM_ENGINE_CLOCK !=
> CISLAND_MINIMUM_ENGINE_CLOCK)
> 3989             pi->need_update_smu7_dpm_table |= DPMTABLE_UPDATE_SCLK;
> 3990    }
>
>  The below patch adds a possibly suitable comment (taken directly from
>  commit d967be9b80a5 ("drm/radeon/ci: disable needless sclk changes")
>  But I´m not sure if such constructs really should be in the upstream
>  kernel at all....
>
> Patch was compile tested with x86_64_defconfig + CONFIG_DRM_RADEON=m
>
> Patch is against 4.7.0-rc7 (localversion-next is -next-20160719)
>
>  drivers/gpu/drm/radeon/ci_dpm.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/radeon/ci_dpm.c b/drivers/gpu/drm/radeon/ci_dpm.c
> index 35e0fc3..7ba4508 100644
> --- a/drivers/gpu/drm/radeon/ci_dpm.c
> +++ b/drivers/gpu/drm/radeon/ci_dpm.c
> @@ -3843,7 +3843,10 @@ static void ci_find_dpm_states_clocks_in_dpm_table(struct radeon_device *rdev,
>         if (i >= sclk_table->count) {
>                 pi->need_update_smu7_dpm_table |= DPMTABLE_OD_UPDATE_SCLK;
>         } else {
> -               /* XXX check display min clock requirements */
> +               /* XXX The current code always reprogrammed the sclk levels,
> +                * but we don't currently handle disp sclk requirements
> +                * so just skip it.
> +                */
>                 if (CISLAND_MINIMUM_ENGINE_CLOCK != CISLAND_MINIMUM_ENGINE_CLOCK)
>                         pi->need_update_smu7_dpm_table |= DPMTABLE_UPDATE_SCLK;
>         }
> --
> 2.1.4
>
>
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