linux-kernel - Re: [PATCH] drm/i915: Avoid bitwise vs logical OR warning in snb_wm_latency

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Date:   Mon, 18 Oct 2021 12:10:40 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Dávid Bolvanský <david.bolvansky@...il.com>
Subject: Re: [PATCH] drm/i915: Avoid bitwise vs logical OR warning in
 snb_wm_latency_quirk()

On Thu, Oct 14, 2021 at 02:21:43PM -0700, Nick Desaulniers wrote:
> On Thu, Oct 14, 2021 at 2:19 PM Nathan Chancellor <nathan@...nel.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 = ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_latency, 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 '|=' 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.

Sure, why not.

> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1473
> > Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> 
> Thanks for the patch!
> Suggested-by: Dávid Bolvanský <david.bolvansky@...il.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> 

Thanks for the patch+review. Applied to drm-intel-next.

> > Signed-off-by: Nathan Chancellor <nathan@...nel.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_private *dev_priv)
> >          * The BIOS provided WM memory latency values are often
> >          * inadequate for high resolution displays. Adjust them.
> >          */
> > -       changed = ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_latency, 12) |
> > -               ilk_increase_wm_latency(dev_priv, dev_priv->wm.spr_latency, 12) |
> > -               ilk_increase_wm_latency(dev_priv, dev_priv->wm.cur_latency, 12);
> > +       changed = ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_latency, 12);
> > +       changed |= ilk_increase_wm_latency(dev_priv, dev_priv->wm.spr_latency, 12);
> > +       changed |= ilk_increase_wm_latency(dev_priv, dev_priv->wm.cur_latency, 12);
> >
> >         if (!changed)
> >                 return;
> >
> > base-commit: d73b17465d6da0a94bc0fcc86b150e1e923e8f71
> > --
> > 2.33.1.637.gf443b226ca
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers

-- 
Ville Syrjälä
Intel