linux-kernel - Re: [PATCH] phy: intel: Eliminate unnecessary assignment in intel_cbphy_set

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Date:   Tue, 26 May 2020 13:52:52 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] phy: intel: Eliminate unnecessary assignment in
 intel_cbphy_set_mode

On Tue, May 26, 2020 at 11:12:58AM -0700, Nick Desaulniers wrote:
> On Fri, May 22, 2020 at 8:51 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > Clang warns:
> >
> > drivers/phy/intel/phy-intel-combo.c:202:34: warning: implicit conversion
> > from enumeration type 'enum intel_phy_mode' to different enumeration
> > type 'enum intel_combo_mode' [-Wenum-conversion]
> >         enum intel_combo_mode cb_mode = PHY_PCIE_MODE;
> >                               ~~~~~~~   ^~~~~~~~~~~~~
> > 1 warning generated.
> >
> > The correct enum to use would be PCIE0_PCIE1_MODE. However, eliminating
> > this assignment is a little better because the switch statement always
> 
> Indeed, the switch is exhaustive.  Might be a risk if new enumeration
> values are added to the enum, though.

Clang will warn about that (and since there is no default case
statement, that would point to a bug).

> Probably should just initialize it to PCIE0_PCIE1_MODE, then you can
> simplify the PHY_PCIE_MODE case a little (replace ternary with
> if+assignment).

I did consider this but every maintainer has their preference around
initializing local variables at the top versus close to their usage...

I do not really have a preference for what happens here, I'm happy to
rework the patch based on maintainer feedback, thanks for the review!

Cheers,
Nathan

> > assigns a new value to cb_mode, which also takes care of the warning.
> >
> > Fixes: ac0a95a3ea78 ("phy: intel: Add driver support for ComboPhy")
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1034
> > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > ---
> >  drivers/phy/intel/phy-intel-combo.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/phy/intel/phy-intel-combo.c b/drivers/phy/intel/phy-intel-combo.c
> > index c2a35be4cdfb..4bc1276ecf23 100644
> > --- a/drivers/phy/intel/phy-intel-combo.c
> > +++ b/drivers/phy/intel/phy-intel-combo.c
> > @@ -199,9 +199,9 @@ static int intel_cbphy_pcie_dis_pad_refclk(struct intel_cbphy_iphy *iphy)
> >
> >  static int intel_cbphy_set_mode(struct intel_combo_phy *cbphy)
> >  {
> > -       enum intel_combo_mode cb_mode = PHY_PCIE_MODE;
> >         enum aggregated_mode aggr = cbphy->aggr_mode;
> >         struct device *dev = cbphy->dev;
> > +       enum intel_combo_mode cb_mode;
> >         enum intel_phy_mode mode;
> >         int ret;
> >
> >
> > base-commit: c11d28ab4a691736e30b49813fb801847bd44e83
> > --
> 
> -- 
> Thanks,
> ~Nick Desaulniers