linux-kernel - Re: [PATCH 3/3] serial: sh-sci: Add reset support for RZ/G2L SoC

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Message-ID: <CAMuHMdWOQq=avCqAU5t+gKqdb5FMRZB2hz7fVNmtgWK8Yp3iWg@mail.gmail.com>
Date:   Tue, 9 Nov 2021 08:49:56 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH 3/3] serial: sh-sci: Add reset support for RZ/G2L SoC

Hi Prabhakar,

On Tue, Nov 9, 2021 at 1:34 AM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
> On Mon, Nov 8, 2021 at 4:40 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Wed, Nov 3, 2021 at 6:31 PM Lad Prabhakar
> > <prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> > > On RZ/G2L devices should be explicitly pulled out of reset for it
> > > to work. This patch adds support to read the "resets" property and
> > > performs deassert/assert when required.
> > >
> > > Also, propagate the error to the caller of sci_parse_dt() instead of
> > > returning NULL in case of failure.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > Reviewed-by: Biju Das <biju.das.jz@...renesas.com>
> >
> > Thanks for your patch!
> >
> > > ---
> > > Hi Geert,
> > > For handling the resets I was in dual mind whether to perform
> > > reset based on compatible strings or soc-id, let me know your
> > > thoughts. Currently no SoC's use "renesas,sci" so using the same
> > > for performing the reset operation for SCI.
> >
> > We do, on H8/300.
> >
> Missed that.
>
> > > --- a/drivers/tty/serial/sh-sci.c
> > > +++ b/drivers/tty/serial/sh-sci.c
> > > @@ -3203,23 +3204,58 @@ static const struct of_device_id of_sci_match[] = {
> > >  };
> > >  MODULE_DEVICE_TABLE(of, of_sci_match);
> > >
> > > +static void sci_reset_control_assert(void *data)
> > > +{
> > > +       reset_control_assert(data);
> > > +}
> > > +
> > >  static struct plat_sci_port *sci_parse_dt(struct platform_device *pdev,
> > >                                           unsigned int *dev_id)
> > >  {
> > >         struct device_node *np = pdev->dev.of_node;
> > > +       const struct of_device_id *of_id;
> > >         struct plat_sci_port *p;
> > >         struct sci_port *sp;
> > >         const void *data;
> > >         int id;
> > >
> > >         if (!IS_ENABLED(CONFIG_OF) || !np)
> > > -               return NULL;
> > > +               return ERR_PTR(-EINVAL);
> > > +
> > > +       of_id = of_match_device(of_sci_match, &pdev->dev);
> > > +       if (!of_id)
> > > +               return ERR_PTR(-EINVAL);
> > >
> > > -       data = of_device_get_match_data(&pdev->dev);
> > > +       if (!strcmp(of_id->compatible, "renesas,scif-r9a07g044") ||
> > > +           !strcmp(of_id->compatible, "renesas,sci")) {
> >
> > This will match on H8/300, too, which doesn't have resets.
> > Please match against "renesas,sci-r9a07g044" instead.
> >
> > Please don't use explicit strcmp() calls here, but add a flag to
> > of_sci_match[].data.
> >
> Agreed, does the below hunk look good for handling the reset?
>
> -#define SCI_OF_DATA(type, regtype)     (void *)((type) << 16 | (regtype))
> +#define SCIx_RESET                             BIT(31)
> +#define SCI_OF_DATA(type, regtype, reset)      (void *)(reset |
> (type) << 16 | (regtype))
>  #define SCI_OF_TYPE(data)              ((unsigned long)(data) >> 16)
>  #define SCI_OF_REGTYPE(data)           ((unsigned long)(data) & 0xffff)
>
> @@ -3169,7 +3170,11 @@ static const struct of_device_id of_sci_match[] = {
>         },
>         {
>                 .compatible = "renesas,scif-r9a07g044",
> -               .data = SCI_OF_DATA(PORT_SCIF, SCIx_RZ_SCIFA_REGTYPE),
> +               .data = SCI_OF_DATA(PORT_SCIF, SCIx_RZ_SCIFA_REGTYPE,
> SCIx_RESET),
> +       },
> +       {
> +               .compatible = "renesas,sci-r9a07g044",
> +               .data = SCI_OF_DATA(PORT_SCI, SCIx_SCI_REGTYPE, SCIx_RESET),
>         },

That's what I had in mind.

But upon second thought, it might be better to just drop the check,
and obtain an optional reset instead?
After all the reset requirement is not a feature of this specific
SCI(F) variant, but an SoC integration feature.  And deasserting
the reset on other SoCs that have a reset should be fine.

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