Re: [PATCH v4 13/15] rtc: rzn1: Add OF match data to gate SUBU register access

[Lad, Prabhakar]

Hi Wolfram,

Thank you for the review.

On Thu, Aug 20, 2026 at 12:20 PM Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, Aug 19, 2026 at 11:39:24AM +0100, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> >
> > The RZ/N1 RTC driver selects SCMP mode only when an optional xtal clock
> > is provided at a valid rate other than 32768 Hz. Without an xtal clock,
> > or when it runs at 32768 Hz, the driver uses SUBU mode.
> >
> > However, the RTCA0SUBU register used by SUBU mode is not present on all
> > SoCs that integrate a similar variant of the RTC block. Allowing SUBU
> > mode on those variants would expose RTC offset operations that access a
> > non-existent register.
> >
> > Add OF match data to describe whether the RTC supports the SUBU register.
> > Reject probe with -EOPNOTSUPP when SUBU mode would be selected on a
> > variant without SUBU support.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
>
> Suggested-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
>
> I still think, this code needs a change:
>
> 454                 if (rate != 32768)
> 455                         scmp_val = RZN1_RTC_CTL0_SLSB_SCMP;
>
>         if (rate != 32768 || !data->has_subu)
>
> otherwise having a xtal with 32768 on a SCMP-only device will not be
> accepted despite it should work.
>
Agreed.

> Haven't checked if that could simplify your later has_subu-check or not.
>
To reduce the checks I can add a else if check like below:

/* Only switch to scmp if we have an xtal clock with a valid rate and
!= 32768 */
xtal = devm_clk_get_optional(dev, "xtal");
if (IS_ERR(xtal)) {
        return PTR_ERR(xtal);
} else if (xtal) {
        rate = clk_get_rate(xtal);

        if (rate < 32000 || rate > BIT(22))
                return -EOPNOTSUPP;

        if (rate != 32768 || !data->has_subu)
                scmp_val = RZN1_RTC_CTL0_SLSB_SCMP;
} else if (!data->has_subu) {
        return dev_err_probe(dev, -EOPNOTSUPP,
                             "No valid XTAL provided and SUBU mode not
supported\n");
}

Cheers,
Prabhakar