RE: [PATCH v4 1/7] dt-bindings: can: renesas,rcar-canfd: Document RZ/G3S SoC

[Biju Das]

Hi Claudiu,

> -----Original Message-----
> From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
> Sent: 16 October 2026 14:34
> Subject: Re: [PATCH v4 1/7] dt-bindings: can: renesas,rcar-canfd: Document RZ/G3S SoC
> 
> On 02.09.2026 17:15:38, Claudiu Beznea wrote:
> > From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> >
> > The CAN FD controller found on the Renesas RZ/G3S SoC is largely
> > compatible with the variant present on the RZ/G3E SoC. The main differences are:
> > - the RZ/G3S provides only two CAN FD channels
> > - the RZ/G3S supports only CAN FD operation; the Channel n CAN FD
> >   Configuration Register does not implement the bits used to select
> >   classical CAN-only mode (bit 30) or CAN FD-only mode (bit 28);
> >   consequently, bit 31 (CAN FD Frame Distinction Enable) of the same
> >   register is also not implemented
> > - some bits in several registers (mainly reserved or status bits) are
> >   read-write on the RZ/G3S but read-only on the RZ/G3E; their behavior is
> >   otherwise identical: the bits read back as 0 on both SoCs and software
> >   is allowed to write only 0 to them on the RZ/G3S
> > - the RZ/G3S provides 256 acceptance filters, compared to 768 on the
> >   RZ/G3E
> > - the RZ/G3S can use PCLK clock as the CAN FD clock source through an
> >   internal clock divider, while also supporting an external CAN FD clock
> >   source
> >
> > Since:
> > - the SoC clock generator provides to the CAN IP only the peripheral and
> >   the RAM clocks
> > - when sourced from the peripheral clock, the CAN-FD clock is obtained
> >   inside the IP itself by dividing the peripheral clock
> > - the assigned-clocks and assigned-clock-rates properties are specific to
> >   the CAN-FD clock
> > the assigned-clocks and assigned-clock-rates properties were dropped
> > from the required properties list of the Renesas RZ/G3S SoC.
> >
> > Add documentation for the Renesas RZ/G3S SoC.
> >
> > Reviewed-by: Rob Herring (Arm) <robh@xxxxxxxxxx>
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> > Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> 
> the netdev review bot has found a nitpick, it's about the comment in "rcar_canfd.c". Can you fix it, if
> you re-spin the series.
> 
> regards,
> Marc
> 
> pw-bot: cr
> 
> --- Patch [11]: [PATCH net-next 11/37] dt-bindings: can: renesas,rcar-canfd: Document RZ/G3S SoC ---
> commit 69b4e37d18e5229e1c800b45a5df061af8a98eb9
> Author: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> 
> dt-bindings: can: renesas,rcar-canfd: Document RZ/G3S SoC
> 
> This adds the renesas,r9a08g045-canfd compatible for the RZ/G3S CAN FD controller. It adds the compatible
> to the existing conditional blocks. It also forbids renesas,no-can-fd and renesas,fd-only on RZ/G3S, and
> makes assigned-clocks and assigned-clock-rates required only for the other SoCs.
> 
> Link: https://patch.msgid.link/20260902141544.565763-2-claudiu.beznea+renesas@xxxxxxxxx
> 
> > diff --git
> > a/Documentation/devicetree/bindings/net/can/renesas,rcar-canfd.yaml
> > b/Documentation/devicetree/bindings/net/can/renesas,rcar-canfd.yaml
> > index b9d9dd7a7967..bbaaef8f4282 100644
> > ---
> > a/Documentation/devicetree/bindings/net/can/renesas,rcar-canfd.yaml
> > +++ b/Documentation/devicetree/bindings/net/can/renesas,rcar-canfd.yam
> > +++ l
> 
> [ ... ]
> 
> > @@ -350,6 +352,20 @@ allOf:
> >        properties:
> >          reset-names: false
> >
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            const: renesas,r9a08g045-canfd
> > +    then:
> > +      properties:
> > +        renesas,no-can-fd: false
> 
> Discovered by: opus-5-5 · Missed by: fable-5-1, gpt-6-astra, sashiko-gemini · Confirmed by: fable-5-1
> This isn't a bug, but should the renesas,no-can-fd description be updated to match this new constraint?
> 
> The property description in the same binding still says that every controller can run in Classical CAN
> mode:
> 
>   renesas,no-can-fd:
>     $ref: /schemas/types.yaml#/definitions/flag
>     description:
>       The controller can operate in either CAN-FD mode (default) or FD-Only
>       mode (RZ/{G2L,G3E} and R-Car Gen4) or Classical CAN mode. Specify this
>       property to put the controller in Classical CAN mode.
> 
> With this patch the property is forbidden for renesas,r9a08g045-canfd, because RZ/G3S does not have the
> mode select bits.
> 
> The header comment in drivers/net/can/rcar/rcar_canfd.c says the same
> thing:
> 
>  * To switch the controller to Classical CAN (CAN 2.0) only mode, add
>  * "renesas,no-can-fd" optional property to the device tree node. A h/w reset is
>  * also required to switch modes.
> 
> Neither text is changed later in the series. Both now contradict the schema for RZ/G3S, and for RZ/G3L
> once it is added the same way.
> 
> Could the description exclude the SoCs that only support CAN FD mode?


Do you plan to update description of renesas,no-canfd in bindings/driver exempting Classical CAN mode
for RZ/G3S? Or do you want me to update?

Please let me know.

Cheers,
Biju