linux-kernel - Re: [PATCH v4 05/12] clk: renesas: clk-vbattb: Add VBATTB clock driver

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Message-ID: <CAMuHMdXQ2DM7Qzcne5KEN2sx1z4PZn=SFkmWwMENkKQfWGGE_A@mail.gmail.com>
Date: Thu, 24 Oct 2024 16:21:52 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Claudiu <claudiu.beznea@...on.dev>
Cc: mturquette@...libre.com, sboyd@...nel.org, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, alexandre.belloni@...tlin.com, 
	magnus.damm@...il.com, p.zabel@...gutronix.de, 
	linux-renesas-soc@...r.kernel.org, linux-clk@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-rtc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH v4 05/12] clk: renesas: clk-vbattb: Add VBATTB clock driver

On Sat, Oct 19, 2024 at 10:47 AM Claudiu <claudiu.beznea@...on.dev> wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>
> The VBATTB IP of the Renesas RZ/G3S SoC controls the clock that is used
> by the RTC. The input to the VBATTB could be a 32KHz crystal
> or an external clock device.
>
> The HW block diagram for the clock generator is as follows:
>
>            +----------+ XC   `\
> RTXIN  --->|          |----->| \       +----+  VBATTCLK
>            | 32K clock|      |  |----->|gate|----------->
>            | osc      | XBYP |  |      +----+
> RTXOUT --->|          |----->| /
>            +----------+      ,
>
> After discussions w/ Stephen Boyd the clock tree associated with this
> hardware block was exported in Linux as:
>
> vbattb-xtal
>    xbyp
>    xc
>       mux
>          vbattbclk
>
> where:
> - input-xtal is the input clock (connected to RTXIN, RTXOUT pins)
> - xc, xbyp are mux inputs
> - mux is the internal mux
> - vbattclk is the gate clock that feeds in the end the RTC
>
> to allow selecting the input of the MUX though assigned-clock DT
> properties, using the already existing clock drivers and avoid adding
> other DT properties. If the crystal is connected on RTXIN,
> RTXOUT pins the XC will be selected as mux input. If an external clock
> device is connected on RTXIN, RTXOUT pins the XBYP will be selected as
> mux input.
>
> The load capacitance of the internal crystal can be configured
> with renesas,vbattb-load-nanofarads DT property.
>
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> ---
>
> Changes in v4:
> - dropped oscillator from patch description
> - s/on-board/internal in patch description
> - updated dt-binding included file name in the driver as it has been
>   renamed to include/dt-bindings/clock/renesas,r9a08g045-vbattb.h
> - dropped the "_BIT" from driver macros
> - used "quartz-load-femtofarads" dt property instead of adding a new one
> - register the "vbattclk" as critical clock as this feeds the RTC counter
>   logic and it needs to stay on from the moment the RTC is configured;
>   along with it, added a comment to express this.

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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