Hi Geert,
> -----Original Message-----
> From: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Sent: mercredi 23 avril 2025 10:52
> To: Thierry Bultel <thierry.bultel.yh@xxxxxxxxxxxxxx>
> Cc: thierry.bultel@xxxxxxxxxxx; linux-renesas-soc@xxxxxxxxxxxxxxx; Paul
> Barker <paul.barker.ct@xxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> linux-clk@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v7 06/13] clk: renesas: Add support for R9A09G077 SoC
>
> Hi Thierry,
>
> On Wed, 23 Apr 2025 at 09:36, Thierry Bultel
> <thierry.bultel.yh@xxxxxxxxxxxxxx> wrote:
> > > From: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> On Fri, 18 Apr 2025
> > > at 23:22, Thierry Bultel <thierry.bultel.yh@xxxxxxxxxxxxxx> wrote:
> > > > +};
> > > > > > +
> > > > > > +static const struct mssr_mod_clk r9a09g077_mod_clks[]
> > > > > > +__initconst =
> > > {
> > > > > > + DEF_MOD("sci0", 108, R9A09G077_PCLKM),
> > > > >
> > > > > Shouldn't that be 8 instead of 108?
> > > > > Using R9A09G077_PCLKM as the parent is a temporary
> > > > > simplification,
> > > right?
> > > >
> > > > I am probably missing something, isn’t PCKML actually the parent
> clock ?
> > >
> > > According to Figure 7.1 ("Block diagram of clock generation
> > > circuit"), it is PCLKSCI0, which can be switched to PCLKM. I guess
> > > that is the default, hence my "temporary simplification" question.
> > >
> > > As the actual switching is controlled through the SCI's CCR3
> > > register, the SCI block should have two clock inputs in DT (PCLKM
> > > and PCLKSCIn), and thus the DT bindings should be amended. See also
> > > Figure 33.1 ("SCI block diagram").
> > >
> >
> > Thanks for clarifying.
> > Indeed, this is the default setting (and the one we have at this stage).
> > I think that support for PCLKSCIn can be added at the time we support
> > baudrate setting.
>
> I am not sure we can do that in a clean backwards-compatible way.
> Currently the DT bindings describe a single clock:
>
> clock-names:
> const: fck # UART functional clock
>
> The documentation calls the two clocks:
> - Bus clock (PCLKM),
> - Operation clock (PCLKSCIn).
>
> Which one is the functional clock? I'd say the latter...
> Currently, DT says:
>
> clocks = <&cpg CPG_MOD 8>;
> clock-names = "fck";
>
> and the clock driver uses PCLKM as the module's parent clock, I think you
> will have a very hard time to synchronize all of the clock driver, sci
> driver, and DTS when transitioning to something like:
>
> clocks = <&cpg CPG_MOD 8>, <&cpgR9A09G077_PCLKM>;
> clock-names = "fck", "bus";
>
> where the modulo clock has to become PCLKSCIn (actually SCInASYNC, as seen
> from the CPG).
>
> Does that make sense, or am I missing something?
You are right, I completely understand how hard it would be to have backward compatibility.
However, doing so:
clocks = <&cpg CPG_MOD R9A09G077_PCLK_SCI0>, <&cpg CPG_CORE R9A09G077_CLK_PCLKM>;
clock-names = "fck", "bus";
without modifying the sh-sci driver (yet) would lead to this bogus clk_summary:
clock count count count rate accuracy phase cycle enable consumer id
---------------------------------------------------------------------------------------------------------------------------------------------
loco 0 0 0 1000000 0 0 50000 Y deviceless no_connection_id
extal 1 1 0 25000000 0 0 50000 Y clock-controller@80280000 extal
deviceless no_connection_id
.pll4 1 1 0 2400000000 0 0 50000 Y deviceless no_connection_id
.sel_pll4 1 1 0 2400000000 0 0 50000 Y deviceless no_connection_id
.sel_clk_pll4 1 1 0 2400000000 0 0 50000 Y deviceless no_connection_id
.pll4d1 1 1 0 2400000000 0 0 50000 Y deviceless no_connection_id
.sci0async 1 1 0 100000000 0 0 50000 Y deviceless no_connection_id
sci0 2 2 0 100000000 0 0 50000 Y 80005000.serial fck
deviceless of_clk_get_from_provider
deviceless no_connection_id
it is wrong because the actual default state is that PCKLM is used, not sci0async.
Having PCKML consumed by sci0 is an obvious fix in sci_init_clocks, but it won't show up that only one clock is used at a time.
Couldn't it be better be solved by introducing an extra mux clock ? (the one controlled by BPEN) ?
Thanks !
Thierry
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
>
> In personal conversations with technical people, I call myself a hacker.
> But when I'm talking to journalists I just say "programmer" or something
> like that.
> -- Linus Torvalds
