linux-kernel - [PATCH v2 5/5] rtc: zynqmp: use dynamic max and min offset ranges

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Message-Id: <20260108-zynqmp-rtc-updates-v2-5-864c161fa83d@vaisala.com>
Date: Thu, 08 Jan 2026 12:51:16 +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>
Subject: [PATCH v2 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.

Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
---
 drivers/rtc/rtc-zynqmp.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c
index d15c256e7ae56058ddc38849af6424cd29b8965e..f508c61f4046e906d9569cc779a1360474a85fd2 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			1000000000LL
-#define RTC_MIN_OFFSET		-32768000
-#define RTC_MAX_OFFSET		32767000
 
 struct xlnx_rtc_dev {
 	struct rtc_device	*rtc;
@@ -215,12 +213,12 @@ static int xlnx_rtc_set_offset(struct device *dev, long offset)
 
 	/* Tick to offset multiplier */
 	tick_mult = DIV_ROUND_CLOSEST(RTC_PPB, xrtcdev->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