Re: [PATCH v5 3/3] hwmon: (pmbus/adm1266) add rtc debugfs entry

[Guenter Roeck]

On Wed, May 20, 2026 at 03:42:42PM -0700, Abdurrahman Hussain wrote:
> The driver seeds the chip's SET_RTC register once at probe with
> ktime_get_real_seconds().  Over a long uptime the chip's internal
> seconds counter drifts away from the host's wall-clock time, so the
> timestamp embedded in each blackbox record stops being meaningful
> in wall-clock terms.  The datasheet recommends that the host
> periodically resynchronise the counter to address this; today the
> driver has no userspace-facing knob for that.
> 
> Expose SET_RTC via an rtc debugfs file alongside the other adm1266
> debugfs entries:
> 
>   read  -- returns the chip's current SET_RTC seconds counter, so
>            userspace can observe how far the chip has drifted from
>            host wall-clock without writing anything.
>   write -- the kernel re-reads ktime_get_real_seconds() itself and
>            pushes it to the chip.  The write payload is ignored;
>            userspace does not get to supply its own timestamp
>            value, so there is no way for it to push a wrong time
>            into the chip.
> 
> A small userspace agent (chrony hook, systemd-timesyncd dispatch
> script, or a periodic cron job) can write to this file to keep the
> chip's counter aligned with wall-clock across long uptimes.
> 
> Both the read and write paths take pmbus_lock to serialise against
> the pmbus_core's own PAGE+register sequences and against the other
> adm1266 debugfs accessors that already run under the same lock.
> 
> While at it, drop the now-redundant adm1266_set_rtc() probe-time
> helper.  The new adm1266_rtc_set() callback does exactly the same
> byte-packing and write; probe just calls adm1266_rtc_set(client, 0)
> (the ignored @val argument) after pmbus_do_probe() so the
> pmbus_lock acquired by the new helper has a live mutex to take.
> 
> Signed-off-by: Abdurrahman Hussain <abdurrahman@xxxxxxxxxx>
> Assisted-by: Claude-Code:claude-opus-4-7
> Assisted-by: sashiko:gemini-3.1-pro-preview

Applied.

Thanks,
Guenter