Re: [PATCH v3 01/12] dt-bindings: clock: renesas,r9a08g045-vbattb: Document VBATTB

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

On 03.09.2024 09:58, Biju Das wrote:
> Hi Claudiu,
> 
>> -----Original Message-----
>> From: Claudiu <claudiu.beznea@tuxon.dev>
>> Sent: Friday, August 30, 2024 2:02 PM
>> Subject: [PATCH v3 01/12] dt-bindings: clock: renesas,r9a08g045-vbattb: Document VBATTB
>>
>> From: Claudiu Beznea <claudiu.beznea.uj@bp.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. Add documentation for it.
>>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>> ---
>>
>> Changes in v3:
>> - moved the file to clock dt bindings directory as it is the
>>   only functionality supported at the moment; the other functionalities
>>   (tamper detector, SRAM) are offered though register spreaded
>>   though the address space of the VBATTB IP and not actually
>>   individual devices; the other functionalities are not
>>   planned to be supported soon and if they will be I think they
>>   fit better on auxiliary bus than MFD
>> - dropped interrupt names as requested in the review process
>> - dropped the inner node for clock controller
>> - added #clock-cells
>> - added rtx clock
>> - updated description for renesas,vbattb-load-nanofarads
>> - included dt-bindings/interrupt-controller/irq.h in examples section
>>
>> Changes in v2:
>> - changed file name and compatible
>> - updated title, description sections
>> - added clock controller part documentation and drop dedicated file
>>   for it included in v1
>> - used items to describe interrupts, interrupt-names, clocks, clock-names,
>>   resets
>> - dropped node labels and status
>> - updated clock-names for clock controller to cope with the new
>>   logic on detecting the necessity to setup bypass
>>
>>  .../clock/renesas,r9a08g045-vbattb.yaml       | 81 +++++++++++++++++++
>>  1 file changed, 81 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/clock/renesas,r9a08g045-vbattb.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/clock/renesas,r9a08g045-vbattb.yaml
>> b/Documentation/devicetree/bindings/clock/renesas,r9a08g045-vbattb.yaml
>> new file mode 100644
>> index 000000000000..29df0e01fae5
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/clock/renesas,r9a08g045-vbattb.y
>> +++ aml
>> @@ -0,0 +1,81 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/clock/renesas,r9a08g045-vbattb.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Renesas Battery Backup Function (VBATTB)
>> +
>> +description:
>> +  Renesas VBATTB is an always on powered module (backed by battery)
>> +which
>> +  controls the RTC clock (VBATTCLK), tamper detection logic and a small
>> +  general usage memory (128B).
>> +
>> +maintainers:
>> +  - Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>> +
>> +properties:
>> +  compatible:
>> +    const: renesas,r9a08g045-vbattb
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  interrupts:
>> +    items:
>> +      - description: tamper detector interrupt
>> +
>> +  clocks:
>> +    items:
>> +      - description: VBATTB module clock
>> +      - description: RTC input clock (crystal oscillator or external
>> + clock device)
>> +
>> +  clock-names:
>> +    items:
>> +      - const: bclk
>> +      - const: rtx
>> +
>> +  '#clock-cells':
>> +    const: 1
>> +
>> +  power-domains:
>> +    maxItems: 1
> 
> Not sure, you need to document "PD_VBATT" power domain 
> as per Table 41.2, this LSI supports 3 power domains(PD_ISOVCC, PD_VCC, PD_VBATT)
> 
> Power Mode PD_ISOVCC PD_VCC PD_VBATT
> ALL_ON      ON          ON    ON
> AWO         OFF         ON    ON
> VBATT       OFF         OFF   ON
> ALL_OFF     OFF         OFF   OFF
> 
> PD_VBATT domain is the area where the RTC/backup register is located, works on battery power when the power of
> PD_VCC and PD_ISOVCC domain are turned off.

In Linux, the CPG is the power domain provider for all the IPs in RZ/G3S
SoC (modeled though MSTOP CPG support). This is how it is currently
implemented.

Then groups of IPs are part of power domains PD_ISOVCC, PD_VCC, PD_VBATT.
These power domains are i2c controlled with the help of firmware (at least
at the moment).

From HW manual:
- PD_VCC domain always powered on area.

- PD_ISOVCC domain is the area where the power can be turned off.

- PD_VBATT domain is the area where the RTC/backup register is located,
  works on battery power when the power of
.

The power to these domains are controlled with the help of firmware. Linux
cannot do control itself as the CPU is in the PD_ISOVCC. If you look at
picture 41.3 Power mode transition [1] it is mentioned the relation b/w
these power domains (controlled by PMIC though firmware) and the supported
power saving modes: ALL_ON, AWO, VBATT.

Thank you,
Claudiu Beznea

[1] https://pasteboard.co/4ureEUnyCfV8.png

> 
> Cheers,
> Biju
> 
>> +
>> +  resets:
>> +    items:
>> +      - description: VBATTB module reset
>> +
>> +  renesas,vbattb-load-nanofarads:
>> +    description: load capacitance of the on board crystal oscillator
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    enum: [ 4000, 7000, 9000, 12500 ]
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - interrupts
>> +  - clocks
>> +  - clock-names
>> +  - '#clock-cells'
>> +  - power-domains
>> +  - resets
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/clock/r9a08g045-cpg.h>
>> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
>> +    #include <dt-bindings/interrupt-controller/irq.h>
>> +
>> +    vbattb@1005c000 {
>> +        compatible = "renesas,r9a08g045-vbattb";
>> +        reg = <0x1005c000 0x1000>;
>> +        interrupts = <GIC_SPI 43 IRQ_TYPE_LEVEL_HIGH>;
>> +        clocks = <&cpg CPG_MOD R9A08G045_VBAT_BCLK>, <&vbattb_xtal>;
>> +        clock-names = "bclk", "rtx";
>> +        #clock-cells = <1>;
>> +        power-domains = <&cpg>;
>> +        resets = <&cpg R9A08G045_VBAT_BRESETN>;
>> +        renesas,vbattb-load-nanofarads = <12500>;
>> +    };
>> --
>> 2.39.2
>>
>