linux-kernel - Re: [PATCH 02/12] dt-bindings: clock: renesas,rzg3s-vbattb-clk: Document the VBATTB clock driver

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Date: Tue, 18 Jun 2024 11:11:30 +0300
From: claudiu beznea <claudiu.beznea@...on.dev>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Conor Dooley <conor@...nel.org>, mturquette@...libre.com,
 sboyd@...nel.org, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 lee@...nel.org, alexandre.belloni@...tlin.com, magnus.damm@...il.com,
 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 02/12] dt-bindings: clock: renesas,rzg3s-vbattb-clk:
 Document the VBATTB clock driver

Hi, Geert,

On 18.06.2024 10:56, Geert Uytterhoeven wrote:
> Hi Claudiu,
> 
> On Tue, Jun 18, 2024 at 9:34 AM claudiu beznea <claudiu.beznea@...on.dev> wrote:
>> On 17.06.2024 18:19, Conor Dooley wrote:
>>> On Mon, Jun 17, 2024 at 10:02:47AM +0300, claudiu beznea wrote:
>>>> On 15.06.2024 15:17, Conor Dooley wrote:
>>>>> On Fri, Jun 14, 2024 at 10:19:22AM +0300, Claudiu wrote:
>>>>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>>>>
>>>>>> The VBATTB IP of the Renesas RZ/G3S SoC controls the clock that feeds
>>>>>> the RTC and the tamper detector. Add documentation for the VBATTB clock
>>>>>> driver.
>>>>>>
>>>>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>>>> ---
>>>>>>  .../clock/renesas,rzg3s-vbattb-clk.yaml       | 90 +++++++++++++++++++
>>>>>>  1 file changed, 90 insertions(+)
>>>>>>  create mode 100644 Documentation/devicetree/bindings/clock/renesas,rzg3s-vbattb-clk.yaml
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/clock/renesas,rzg3s-vbattb-clk.yaml b/Documentation/devicetree/bindings/clock/renesas,rzg3s-vbattb-clk.yaml
>>>>>> new file mode 100644
>>>>>> index 000000000000..ef52a0c0f874
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/clock/renesas,rzg3s-vbattb-clk.yaml
>>>>>> +  renesas,vbattb-osc-bypass:
>>>>>> +    description: set when external clock is connected to RTXOUT pin
> 
> FTR, this contradicts the explanation below, which states the external
> clock oscillator is connected to RTXIN.

I agree.

> 
>>>>>> +    type: boolean
>>>>>
>>>>> When you say "external clock", is that an input or an output?
>>>>
>>>> I took that statement from the HW manual. As of the HW manual [1], table
>>>> 42.2, that would be an input.
>>>
>>> Forgive me for not wanting to open the zip etc and find the information
>>> in the document, but why do you need an extra property? Is it not
>>> something you can determine from the clocks/clock-names properties?
>>
>> It can't be determined from clocks/clock-names as of my understanding. It
>> depends on the type of the input clock (crystal oscillator or external
>> hardware device generating the clock).
>>
>>> It sounds like an additional clock from your description, is it actually
>>> different way to provide the second clock you mention above?
>>
>> This is the block diagram (see [1], only picture this time) of the module
>> controlling the clock. Please open it, it helps in understanding what I'll
>> explain above.
>>
>> The VBATTB blocks controlling the VBATTBCLK are:
>> - 32KHz-clock oscillator
>> - the mux controlled by BKSCCR.SOSEL
>> - the gate who's input is the mux output and XOSCCR.OUTEN
>>
>> To the 32 KHz-clock oscillator block could be connected:
>> 1/ either a crystal oscillator in which case it will be connected to both
>> RTXIN and RTXOUT pins (the direction of RTXOUT is wrong in this picture for
>> this case)
>> 2/ or a device (like [2]) generating a clock which has a single output and,
>> from my understanding and experience with devices like this, only RTXIN is
>> needed, RTXOUT is connected to the ground; for this case the 32KHz-clock
>> oscillator block from [1] need to be bypassed in which case the newly
>> introduced property will be used; this will select the XBYP on the mux.
> 
> Sounds similar to the RAA215300 PMIC, which includes an ISL1208-derived
> RTC, where this was handled using two different clock names:
> https://elixir.bootlin.com/linux/v6.10-rc1/source/Documentation/devicetree/bindings/regulator/renesas,raa215300.yaml#L49
> https://elixir.bootlin.com/linux/v6.10-rc1/source/drivers/rtc/rtc-isl1208.c#L869

Yes, seem similar. I wasn't aware of this approach. I'll switch to it.

Thank  you,
Claudiu Beznea

> 
> Gr{oetje,eeting}s,
> 
>                         Geert
>