Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20201219125344.671832095@linuxfoundation.org> <20201219125345.376925474@linuxfoundation.org>
 <20201219215139.GA29536@amd> <CAFBinCBRe3Oacqce1EDQpoNmEhXeUxJrA43RTA0+_fVciDJzhg@mail.gmail.com>
 <20201219231312.GA4206@duo.ucw.cz>
In-Reply-To: <20201219231312.GA4206@duo.ucw.cz>
From:   Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Date:   Mon, 21 Dec 2020 15:31:49 +0100
Message-ID: <CAFBinCAxa8=bc8CkLzBpjEUL9usBVZ4YVKxRNG6Bv31ao-7Nfw@mail.gmail.com>
Subject: Re: [PATCH 5.9 14/49] net: stmmac: dwmac-meson8b: fix mask definition
 of the m250_sel mux
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Jerome Brunet <jbrunet@baylibre.com>,
        Jakub Kicinski <kuba@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Pavel,

On Sun, Dec 20, 2020 at 12:13 AM Pavel Machek <pavel@ucw.cz> wrote:
>
> On Sat 2020-12-19 23:38:25, Martin Blumenstingl wrote:
> > Hi Pavel,
> >
> > On Sat, Dec 19, 2020 at 10:51 PM Pavel Machek <pavel@ucw.cz> wrote:
> > [...]
> > > I can't say I like this one:
> > >
> > >
> > > >       clk_configs->m250_mux.reg = dwmac->regs + PRG_ETH0;
> > > > -     clk_configs->m250_mux.shift = PRG_ETH0_CLK_M250_SEL_SHIFT;
> > > > -     clk_configs->m250_mux.mask = PRG_ETH0_CLK_M250_SEL_MASK;
> > > > +     clk_configs->m250_mux.shift = __ffs(PRG_ETH0_CLK_M250_SEL_MASK);
> > >
> > > It replaces constant with computation done at runtime; compiler can't
> > > optimize it as __ffs is implemented with asm().
> > what do you suggest to use instead?
> > personally I don't see a problem because this is only called once at
> > driver probe time.
>
> I believe canonical solution is version before this patch, just with
> fixed values....
OK, thanks for the hint
I will keep it in my for patches in the future


Best regards,
Martin