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

[Biju Das]

Hi Claudiu,

> -----Original Message-----
> From: claudiu beznea <claudiu.beznea at tuxon.dev>
> Sent: Tuesday, September 3, 2024 8:28 AM
> Subject: Re: [PATCH v3 01/12] dt-bindings: clock: renesas,r9a08g045-vbattb: Document VBATTB
> 
> 
> 
> On 03.09.2024 09:58, Biju Das wrote:
> > Hi Claudiu,
> >
> >> -----Original Message-----
> >> From: Claudiu <claudiu.beznea at 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 at 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 at 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.ya
> >> ml
> >> b/Documentation/devicetree/bindings/clock/renesas,r9a08g045-vbattb.ya
> >> ml
> >> new file mode 100644
> >> index 000000000000..29df0e01fae5
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/clock/renesas,r9a08g045-vbatt
> >> +++ b.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 at 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.
> 

DT describes hardware. So, the question was, from that perspective, do we need to document PD_VBATT domain,
as it can be controlled outside linux??

Cheers,
Biju