linux-kernel - Re: [PATCH v5 01/10] dt-bindings: clock: renesas,r9a08g045-vbattb: Document VBATTB

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Message-ID: <bt7kgzreebwyeyfsii2q6fci34vfqst6hrxk6anp6tzthlmc5o@t2ifzexazta7>
Date: Thu, 31 Oct 2024 08:46:30 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Claudiu <claudiu.beznea@...on.dev>
Cc: geert+renesas@...der.be, 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 v5 01/10] dt-bindings: clock: renesas,r9a08g045-vbattb:
 Document VBATTB

On Wed, Oct 30, 2024 at 01:01:11PM +0200, Claudiu wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> 
> The VBATTB IP of the Renesas RZ/G3S SoC controls the clock for RTC,
> the tamper detector and a small general usage memory of 128B.
> 
> The VBATTB controller controls the clock for the RTC on the Renesas
> RZ/G3S. The HW block diagram for the clock logic is as follows:
> 
>            +----------+ XC   `\
> RTXIN  --->|          |----->| \       +----+  VBATTCLK
>            | 32K clock|      |  |----->|gate|----------->
>            | osc      | XBYP |  |      +----+
> RTXOUT --->|          |----->| /
>            +----------+      ,/
> 
> One could connect as input to this HW block either a crystal or
> an external clock device. This is board specific.
> 
> After discussions w/ Stephen Boyd the clock tree associated with this
> hardware block was exported in Linux as:
> 
> input-xtal
>   xbyp
>   xc
>      mux
>         vbattclk
> 
> 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.
> 
> This allows select the input of the mux based on the type of the
> connected input clock:
> - if the 32768 crystal is connected as input for the VBATTB,
>   the input of the mux should be xc
> - if an external clock device is connected as input for the VBATTB the
>   input of the mux should be xbyp
> 
> Add bindings for the VBATTB controller.
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> ---
> 
> Changes in v5:
> - used spaces in the diagram from the patch description
> - added "This is board specific" in the board description to emphasize
>   the usage of the assigned-clocks in the example
> - added default for quartz-load-femtofarads
> - collected tags

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>

Best regards,
Krzysztof