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References: <20211014211916.3550122-1-nathan@kernel.org>
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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 14 Oct 2021 14:21:43 -0700
Message-ID: <CAKwvOdmSFP98Mc1u2b+=_Dux9eB_yumRvxOx7UTXuyXOYzG3uA@mail.gmail.com>
Subject: Re: [PATCH] drm/i915: Avoid bitwise vs logical OR warning in snb_wm_latency_quirk()
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        =?UTF-8?B?RMOhdmlkIEJvbHZhbnNrw70=?= <david.bolvansky@gmail.com>
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On Thu, Oct 14, 2021 at 2:19 PM Nathan Chancellor <nathan@kernel.org> wrote=
:
>
> A new warning in clang points out a place in this file where a bitwise
> OR is being used with boolean types:
>
> drivers/gpu/drm/i915/intel_pm.c:3066:12: warning: use of bitwise '|' with=
 boolean operands [-Wbitwise-instead-of-logical]
>         changed =3D ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_la=
tency, 12) |
>                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=
~~~~~~~~~~
>
> This construct is intentional, as it allows every one of the calls to
> ilk_increase_wm_latency() to occur (instead of short circuiting with
> logical OR) while still caring about the result of each call.
>
> To make this clearer to the compiler, use the '|=3D' operator to assign
> the result of each ilk_increase_wm_latency() call to changed, which
> keeps the meaning of the code the same but makes it obvious that every
> one of these calls is expected to happen.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1473
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>

Thanks for the patch!
Suggested-by: D=C3=A1vid Bolvansk=C3=BD <david.bolvansky@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel=
_pm.c
> index f90fe39cf8ca..aaa3a0998e4c 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3050,9 +3050,9 @@ static void snb_wm_latency_quirk(struct drm_i915_pr=
ivate *dev_priv)
>          * The BIOS provided WM memory latency values are often
>          * inadequate for high resolution displays. Adjust them.
>          */
> -       changed =3D ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_la=
tency, 12) |
> -               ilk_increase_wm_latency(dev_priv, dev_priv->wm.spr_latenc=
y, 12) |
> -               ilk_increase_wm_latency(dev_priv, dev_priv->wm.cur_latenc=
y, 12);
> +       changed =3D ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_la=
tency, 12);
> +       changed |=3D ilk_increase_wm_latency(dev_priv, dev_priv->wm.spr_l=
atency, 12);
> +       changed |=3D ilk_increase_wm_latency(dev_priv, dev_priv->wm.cur_l=
atency, 12);
>
>         if (!changed)
>                 return;
>
> base-commit: d73b17465d6da0a94bc0fcc86b150e1e923e8f71
> --
> 2.33.1.637.gf443b226ca
>


--=20
Thanks,
~Nick Desaulniers