linux-kernel - Re: [PATCH 5.9 14/49] net: stmmac: dwmac-meson8b: fix mask definition of the m250

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Date:   Mon, 21 Dec 2020 15:31:49 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jerome Brunet <jbrunet@...libre.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH 5.9 14/49] net: stmmac: dwmac-meson8b: fix mask definition
 of the m250_sel mux

Hi Pavel,

On Sun, Dec 20, 2020 at 12:13 AM Pavel Machek <pavel@....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@....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