linux-kernel - [PATCH v4 5/5] rtc: zynqmp: use dynamic max and min offset ranges

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Message-Id: <20260122-zynqmp-rtc-updates-v4-5-d4edb966b499@vaisala.com>
Date: Thu, 22 Jan 2026 13:53:49 +0000
From: Tomas Melin <tomas.melin@...sala.com>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 Michal Simek <michal.simek@....com>
Cc: linux-rtc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, Tomas Melin <tomas.melin@...sala.com>, 
 Harini T <harini.t@....com>
Subject: [PATCH v4 5/5] rtc: zynqmp: use dynamic max and min offset ranges

Maximum and minimum offsets in ppb that can be handled are dependent on
the rtc clock frequency and what can fit in the 16-bit register field.

Reviewed-by: Harini T <harini.t@....com>
Tested-by: Harini T <harini.t@....com>
Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
---
 drivers/rtc/rtc-zynqmp.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c
index f0f5dc63e254799ed99927c259c767b30ee877a4..2ae54804b87a47642d118789dc33191c53b36932 100644
--- a/drivers/rtc/rtc-zynqmp.c
+++ b/drivers/rtc/rtc-zynqmp.c
@@ -44,8 +44,6 @@
 #define RTC_FR_MASK		0xF0000
 #define RTC_FR_MAX_TICKS	16
 #define RTC_PPB			1000000000
-#define RTC_MIN_OFFSET		-32768000
-#define RTC_MAX_OFFSET		32767000
 
 struct xlnx_rtc_dev {
 	struct rtc_device	*rtc;
@@ -215,12 +213,13 @@ static int xlnx_rtc_set_offset(struct device *dev, long offset)
 
 	/* Tick to offset multiplier */
 	tick_mult = DIV_ROUND_CLOSEST(RTC_PPB, freq);
-	if (offset < RTC_MIN_OFFSET || offset > RTC_MAX_OFFSET)
-		return -ERANGE;
 
 	/* Number ticks for given offset */
 	max_tick = div_s64_rem(offset, tick_mult, &fract_offset);
 
+	if (freq + max_tick > RTC_TICK_MASK || (freq + max_tick < 1))
+		return -ERANGE;
+
 	/* Number fractional ticks for given offset */
 	if (fract_offset) {
 		fract_part = DIV_ROUND_UP(tick_mult, RTC_FR_MAX_TICKS);

-- 
2.47.3