Re: [PATCH v5 03/10] clk: renesas: clk-vbattb: Add VBATTB clock driver

[Claudiu Beznea <claudiu.beznea@tuxon.dev>]

Hi, Geert, Krzysztof,

On 31.10.2024 10:43, Geert Uytterhoeven wrote:
> Hi Krzysztof,
> 
> On Thu, Oct 31, 2024 at 8:48 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>> On Wed, Oct 30, 2024 at 01:01:13PM +0200, Claudiu wrote:
>>> From: Claudiu Beznea <claudiu.beznea.uj@bp.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.
>>>
>>> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> 
>>> --- a/drivers/clk/renesas/Kconfig
>>> +++ b/drivers/clk/renesas/Kconfig
>>> @@ -237,6 +237,10 @@ config CLK_RZV2H
>>>       bool "RZ/V2H(P) family clock support" if COMPILE_TEST
>>>       select RESET_CONTROLLER
>>>
>>> +config CLK_RENESAS_VBATTB
>>> +     bool "Renesas VBATTB clock controller"
>>
>> tristate
> 
> Good point.
> However, does it work as a module, or would that break the RTC?

On RZ/G3S the RTC counter needs the clock provided by VBATTB.

I'll try with this as a module.

> 
> And this is missing
> 
>         depends on ARCH_RENESAS || COMPILE_TEST
> 
> which I can add while applying.

Thank you!

Claudiu

> 
>>
>>> +     select RESET_CONTROLLER
>>> +
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
>