linux-kernel - [PATCH] rtc: add BSM flags descriptions

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Message-Id: <20250721153332.2177134-1-hugo@hugovil.com>
Date: Mon, 21 Jul 2025 11:33:31 -0400
From: Hugo Villeneuve <hugo@...ovil.com>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: hugo@...ovil.com,
	Hugo Villeneuve <hvilleneuve@...onoff.com>,
	linux-rtc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] rtc: add BSM flags descriptions

From: Hugo Villeneuve <hvilleneuve@...onoff.com>

It is hard to decipher what the RTC BSM flags mean, so add
meaningful descriptions.

Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
---
 include/uapi/linux/rtc.h | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/rtc.h b/include/uapi/linux/rtc.h
index 97aca4503a6a..da65130e316d 100644
--- a/include/uapi/linux/rtc.h
+++ b/include/uapi/linux/rtc.h
@@ -141,10 +141,15 @@ struct rtc_param {
 #define RTC_PARAM_CORRECTION		1
 #define RTC_PARAM_BACKUP_SWITCH_MODE	2
 
+/* Backup switch mode */
 #define RTC_BSM_DISABLED	0
-#define RTC_BSM_DIRECT		1
-#define RTC_BSM_LEVEL		2
-#define RTC_BSM_STANDBY		3
+#define RTC_BSM_DIRECT		1 /* Switch if Vbackup > Vdd */
+#define RTC_BSM_LEVEL		2 /* Switch based on a threshold, usually with an hysteresis */
+#define RTC_BSM_STANDBY		3 /*
+				   * Switch if Vdd > Vbackup.
+				   * Useful to ensure the RTC doesn't draw any
+				   * power until the device is first powered on.
+				   */
 
 #define RTC_MAX_FREQ	8192
 

base-commit: 0bafe291cb429d39b5ff70bcf7b2f3ab026dcb02
-- 
2.39.5