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Date:   Thu, 10 Oct 2019 13:37:36 +0000
From:   Fabrizio Castro <fabrizio.castro@...renesas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>
Subject: RE: [PATCH net-next 2/3] dt-bindings: can: rcar_canfd: document
 r8a774b1 support

Hi Geert,

Thank you for your feedback!

> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Sent: 10 October 2019 13:47
> Subject: Re: [PATCH net-next 2/3] dt-bindings: can: rcar_canfd: document r8a774b1 support
> 
> Hi Fabrizio,
> 
> On Thu, Oct 10, 2019 at 2:37 PM Fabrizio Castro
> <fabrizio.castro@...renesas.com> wrote:
> > Document the support for rcar_canfd on R8A774B1 SoC devices.
> >
> > Signed-off-by: Fabrizio Castro <fabrizio.castro@...renesas.com>
> 
> Thanks for your patch!
> 
> > --- a/Documentation/devicetree/bindings/net/can/rcar_canfd.txt
> > +++ b/Documentation/devicetree/bindings/net/can/rcar_canfd.txt
> > @@ -5,6 +5,7 @@ Required properties:
> >  - compatible: Must contain one or more of the following:
> >    - "renesas,rcar-gen3-canfd" for R-Car Gen3 and RZ/G2 compatible controllers.
> >    - "renesas,r8a774a1-canfd" for R8A774A1 (RZ/G2M) compatible controller.
> > +  - "renesas,r8a774b1-canfd" for R8A774B1 (RZ/G2N) compatible controller.
> >    - "renesas,r8a774c0-canfd" for R8A774C0 (RZ/G2E) compatible controller.
> >    - "renesas,r8a7795-canfd" for R8A7795 (R-Car H3) compatible controller.
> >    - "renesas,r8a7796-canfd" for R8A7796 (R-Car M3-W) compatible controller.
> 
> The above looks good, but I think you forgot to add R8A774B1 to the
> paragraph talking about the CAN FD clock below.

I most certainly did forget to add the R8A774B1 to the CAN FD clock paragraph.
Thank you for pointing this out, will send a v2.

> With that fixed:
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> 
> While at it, the example in the bindings says the CANFD clock should be
> configured to 40 MHz, which matches what is used in the various DTS files.
> However, the Hardware User's Manual states it should be 80 MHz, except
> for R-Car D3.
> Is that correct?

The manual states 80 MHz, and I did test the IP in CAN and CAN FD mode at 80 MHz
a while back, but Ramesh reported some instability at 80 MHz when he first brought
CAN FD up. We don't know if the instability was due to the IP or to the board he was
using, at some point it would be nice to retest the same thing on a different SoC/board
connected to the same peripheral he was using for testing, and see if we get the same
issues. For the time being, to be on the safe side of things, we would like to keep the
clock configured at 40MHz.

Thanks,
Fab

> 
> Thanks!
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds

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