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

Wolfram Sang <[email protected]> Thu, 20 Aug 2026 13:20:42 +0200

Newsgroups	org.kernel.vger.linux-renesas-soc,org.kernel.vger.linux-devicetree,org.kernel.vger.linux-kernel,org.kernel.vger.linux-rtc
Message-ID	<aobjCr7ZtpLmL3VP@ninjato>

On Wed, Aug 19, 2026 at 11:39:24AM +0100, Prabhakar wrote:
> From: Lad Prabhakar <[email protected]>
> 
> 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 <[email protected]>

Suggested-by: Wolfram Sang <[email protected]>

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.

Haven't checked if that could simplify your later has_subu-check or not.

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