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Subject: Re: [PATCH v2 14/15] drivers: thermal: tsens: Create function to return sign-extended temperature
To:     Amit Kucheria <amit.kucheria@linaro.org>
From:   Stephen Boyd <swboyd@chromium.org>
User-Agent: alot/0.8.1
Date:   Wed, 28 Aug 2019 08:44:39 -0700
Sender: linux-kernel-owner@vger.kernel.org
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Quoting Amit Kucheria (2019-08-28 03:35:28)
> (Resending, replied only to Stephen by mistake)
>=20
> On Wed, Aug 28, 2019 at 6:08 AM Stephen Boyd <swboyd@chromium.org> wrote:
> >
> > Quoting Amit Kucheria (2019-08-27 05:14:10)
> > > @@ -310,6 +328,10 @@ int __init init_common(struct tsens_priv *priv)
> > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 =C2=A0 goto err_put_device;
> > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 }
> > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 }
> > > +
> > > + =C2=A0 =C2=A0 =C2=A0 /* Save away resolution of signed temperature =
value for this IP */
> > > + =C2=A0 =C2=A0 =C2=A0 priv->tempres =3D priv->fields[LAST_TEMP_0].ms=
b - priv->fields
> [LAST_TEMP_0].lsb;
> > > +
> >
> > Why not just calculate this in the function that uses it? Is there a
> > reason to stash it away in the struct?
>=20
> To avoid recalculating in an often-called function. It doesn't change for=
 an IP
> version.
>=20
> We can't make it static either inside that function since the initializer=
 isn't
> constant.
>=20

This sounds like a super micro optimization. It's a couple derefs and a
subtraction. If it isn't used anywhere else please just move it into the
function where it's used.