Received-SPF: pass (google.com: domain of linux-kernel+bounces-103559-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
References: <898aa0925a9598d44721d00145015b215434cb3b.1710414195.git.geert@linux-m68k.org>
 <695ebdde-3dc3-41b1-b20b-f02c4ba1ae5d@sifive.com> <CAMuHMdURtL1u-MDXBhiwOfX+zBnuunZYvjt+3GMOp6Y6pj1Efw@mail.gmail.com>
 <42c3d591-abe5-4343-9a94-f1705430dcea@sifive.com>
In-Reply-To: <42c3d591-abe5-4343-9a94-f1705430dcea@sifive.com>
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Thu, 14 Mar 2024 17:16:03 +0100
Message-ID: <CAMuHMdWLuK=SvwW-MvmCc4hhPTChDzU6q6SPCFTzjGFe8oijig@mail.gmail.com>
Subject: Re: [PATCH] clk: starfive: jh7100: Use provided clocks instead of
 hardcoded names
To: Samuel Holland <samuel.holland@sifive.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>, linux-clk@vger.kernel.org, 
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, 
	Emil Renner Berthing <kernel@esmil.dk>, Hal Feng <hal.feng@starfivetech.com>, 
	Michael Turquette <mturquette@baylibre.com>, Stephen Boyd <sboyd@kernel.org>, 
	Paul Walmsley <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>, Conor Dooley <conor.dooley@microchip.com>, 
	Andy Shevchenko <andy.shevchenko@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Samuel,

On Thu, Mar 14, 2024 at 3:56=E2=80=AFPM Samuel Holland
<samuel.holland@sifive.com> wrote:
> On 2024-03-14 9:48 AM, Geert Uytterhoeven wrote:
> > On Thu, Mar 14, 2024 at 3:32=E2=80=AFPM Samuel Holland
> > <samuel.holland@sifive.com> wrote:
> >> On 2024-03-14 6:05 AM, Geert Uytterhoeven wrote:
> >>> The Starfive JH7100 clock driver does not use the DT "clocks" propert=
y
> >>> to find its external input clocks, but instead relies on the names of
> >>> the actual external clock providers.  This is fragile, and caused
> >>> breakage when sanitizing clock names in DT.
> >>>
> >>> Fix this by obtaining the external input clocks through the DT "clock=
s"
> >>> property, and using their clk_hw objects or corresponding name.
> >>>
> >>> Fixes: f03606470886 ("riscv: dts: starfive: replace underscores in no=
de names")
> >>> Fixes: 4210be668a09ee20 ("clk: starfive: Add JH7100 clock generator d=
river")
> >>> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> >
> >>> --- a/drivers/clk/starfive/clk-starfive-jh7100.c
> >>> +++ b/drivers/clk/starfive/clk-starfive-jh7100.c
> >
> >>> @@ -298,13 +311,23 @@ static int __init clk_starfive_jh7100_probe(str=
uct platform_device *pdev)
> >>>       if (IS_ERR(priv->base))
> >>>               return PTR_ERR(priv->base);
> >>>
> >>> +     for (idx =3D 0; idx < EXT_NUM_CLKS; idx++) {
> >>> +             clk =3D devm_clk_get(&pdev->dev, jh7100_ext_clk[idx]);
> >>> +             if (IS_ERR(clk))
> >>> +                     return PTR_ERR(clk);
> >>> +
> >>> +             priv->ext[idx] =3D __clk_get_hw(clk);
> >>> +     }
> >>> +
> >>> +     osc_sys =3D clk_hw_get_name(priv->ext[EXT_CLK_OSC_SYS]);
> >>> +
> >>>       priv->pll[0] =3D devm_clk_hw_register_fixed_factor(priv->dev, "=
pll0_out",
> >>> -                                                      "osc_sys", 0, =
40, 1);
> >>> +                                                      osc_sys, 0, 40=
, 1);
> >>>       if (IS_ERR(priv->pll[0]))
> >>>               return PTR_ERR(priv->pll[0]);
> >>>
> >>>       priv->pll[1] =3D devm_clk_hw_register_fixed_factor(priv->dev, "=
pll1_out",
> >>> -                                                      "osc_sys", 0, =
64, 1);
> >>> +                                                      osc_sys, 0, 64=
, 1);
> >>
> >> These should use devm_clk_hw_register_fixed_factor_parent_hw(). (Or yo=
u could
> >
> > Thanks, I didn't know about that function!
> >
> >> define a devm_clk_hw_register_fixed_factor_fw_name() and drop the othe=
r changes.)
> >
> > Sorry, I don't understand what you mean here?
>
> In the loop below, the parents are already referenced via .fw_name. That =
means
> the string is the DT clock-names property value, not the Linux-internal c=
lock
> name (see clk_core_get()). These two function calls are the only ones tha=
t
> depend on the internal clock name. If you change them to use .fw_name as =
well,
> the clk_core_get() will do the right thing, and you don't need to manuall=
y call
> devm_clk_get().

Thank you, I wasn't aware these fw_name names were actually doing the
right thing ;-)

Still, looking up by name is more expensive than just using the passed
clk_hw.  As there are multiple occurrences of the four external
clocks in the clocks table, thus involving multiple look-ups, I think
it's better to use clk_hw everywhere.

I will update for v2...

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds