Re: [PATCH v15 4/6] reboot: extend psc_reason with power-on and reset causes

[Matti Vaittinen <mazziesaccount@gmail.com>]

On 24/09/2026 10:08, Faruque Ansari wrote:
> psc_reason covered only the protection reasons. Extend it to mirror the
> full POWER_ON_REASON_* vocabulary - power-on, watchdog, software,
> external, RTC, reset button, CPU clock and crystal failures - so a
> provider can report why the system last powered on, not only why it was
> shut down. New values are appended to keep the existing numeric ABI.
> 
> Co-developed-by: Oleksij Rempel <o.rempel@pengutronix.de>
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
> Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
> 
> changes v15:
> - add a static_assert() tying ARRAY_SIZE(psc_reason_descs) to
>    PSCR_REASON_COUNT, so a future enum addition without a matching
>    table entry fails the build instead of silently reading a hole
>    (Matti Vaittinen)
> - Add Reviewed-by tags from Matti Vaittinen.
> changes v12:
> - new patch
> ---
>   include/linux/reboot.h | 28 ++++++++++++++++++++++++++++
>   kernel/reboot.c        | 12 ++++++++++++
>   2 files changed, 40 insertions(+)
> 
> diff --git a/include/linux/reboot.h b/include/linux/reboot.h
> index 4c5327dd7645..13f004ad1066 100644
> --- a/include/linux/reboot.h
> +++ b/include/linux/reboot.h
> @@ -225,9 +225,28 @@ extern void orderly_reboot(void);
>    *	management errors, or an unrecoverable hardware fault requiring
>    *	immediate response.
>    *
> + * @PSCR_POWER_ON: Regular cold power-on (e.g. via a PMIC power-on request).
> + *
> + * @PSCR_WATCHDOG: Reset caused by a watchdog timeout.
> + *
> + * @PSCR_SOFTWARE: Software-initiated reset or reboot.
> + *
> + * @PSCR_EXTERNAL: Reset asserted through an external pin or reset input.
> + *
> + * @PSCR_RTC: Wake-up or power-on triggered by the RTC.
> + *
> + * @PSCR_RESET_BUTTON: Reset triggered by a user reset button.
> + *
> + * @PSCR_CPU_CLK_FAIL: Reset caused by a CPU clock failure.
> + *
> + * @PSCR_XTAL_FAIL: Reset caused by a crystal oscillator failure.
> + *
>    * @PSCR_REASON_COUNT: Number of defined power state change reasons. This
>    *	value is useful for range checking and potential future extensions
>    *	while maintaining compatibility.
> + *
> + * The reasons mirror the POWER_ON_REASON_* strings in
> + * <linux/power/power_on_reason.h>; keep the two in sync when extending.
>    */
>   enum psc_reason {
>   	PSCR_UNKNOWN,
> @@ -236,6 +255,15 @@ enum psc_reason {
>   	PSCR_REGULATOR_FAILURE,
>   	PSCR_OVER_TEMPERATURE,
>   	PSCR_EC_PANIC,
> +	/* Append new reasons here; the numeric order is ABI. */
> +	PSCR_POWER_ON,
> +	PSCR_WATCHDOG,
> +	PSCR_SOFTWARE,
> +	PSCR_EXTERNAL,
> +	PSCR_RTC,
> +	PSCR_RESET_BUTTON,
> +	PSCR_CPU_CLK_FAIL,
> +	PSCR_XTAL_FAIL,
>   
>   	/* Number of reasons */
>   	PSCR_REASON_COUNT,
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index e53fb31bad06..7094c7a8f315 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -7,7 +7,9 @@
>   
>   #define pr_fmt(fmt)	"reboot: " fmt
>   
> +#include <linux/array_size.h>
>   #include <linux/atomic.h>
> +#include <linux/build_bug.h>
>   #include <linux/ctype.h>
>   #include <linux/export.h>
>   #include <linux/kexec.h>
> @@ -1102,7 +1104,17 @@ static const struct psc_reason_desc psc_reason_descs[] = {
>   	[PSCR_REGULATOR_FAILURE] = { "regulator-failure", POWER_ON_REASON_REGULATOR_FAILURE },
>   	[PSCR_OVER_TEMPERATURE]	 = { "over-temperature",  POWER_ON_REASON_OVER_TEMPERATURE },
>   	[PSCR_EC_PANIC]		 = { "ec-panic",	  POWER_ON_REASON_EC_PANIC },
> +	[PSCR_POWER_ON]		 = { "power-on",	  POWER_ON_REASON_REGULAR },
> +	[PSCR_WATCHDOG]		 = { "watchdog",	  POWER_ON_REASON_WATCHDOG },
> +	[PSCR_SOFTWARE]		 = { "software",	  POWER_ON_REASON_SOFTWARE },
> +	[PSCR_EXTERNAL]		 = { "external",	  POWER_ON_REASON_EXTERNAL },
> +	[PSCR_RTC]		 = { "rtc",		  POWER_ON_REASON_RTC },
> +	[PSCR_RESET_BUTTON]	 = { "reset-button",	  POWER_ON_REASON_RST_BTN },
> +	[PSCR_CPU_CLK_FAIL]	 = { "cpu-clock-failure", POWER_ON_REASON_CPU_CLK_FAIL },
> +	[PSCR_XTAL_FAIL]	 = { "crystal-failure",	  POWER_ON_REASON_XTAL_FAIL },
>   };
> +static_assert(ARRAY_SIZE(psc_reason_descs) == PSCR_REASON_COUNT,
> +	      "psc_reason_descs[] must have an entry for every psc_reason");

Thanks Faruque. This is better than nothing, but if I read it right, it 
won't still catch missing initializations when last item is initialized 
(but not all items). Eg:

enum {
	PSCR_REGULATOR_FAILURE,
	PSCR_OVER_TEMPERATURE,
	PSCR_EC_PANIC,
	...
	PSCR_REASON_COUNT
};

static const struct psc_reason_desc psc_reason_descs[] = {
	[ PSCR_REASON_COUNT - 1] = { "foo", BAR }
};

static_assert(ARRAY_SIZE(psc_reason_descs) == PSCR_REASON_COUNT,
	      "psc_reason_descs[] must have an entry for every psc_reason");

would pass the check, but accessors would crash to uninitialized 
entries. Hence, I would still prefer the run-time NULL checks.

Oh, and I just noticed there is comma following the 'PSCR_REASON_COUNT' 
in the enum. Since 'PSCR_REASON_COUNT' should always be kept as the last 
enum value, the comma should be omitted.

Other than this - I like the changes you implemented this series. Won't 
reply to other patches, but I think this is a very nice series!

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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