Hi,

On 09/12/2025 21:28, T, Harini wrote:

[Public]

Hi,

quoted

-----Original Message-----
From: Tomas Melin <redacted>
Sent: Monday, December 1, 2025 6:20 PM
To: Alexandre Belloni <alexandre.belloni@bootlin.com>; Simek, Michal
[off-list ref]
Cc: linux-rtc@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-
kernel@vger.kernel.org; Tomas Melin [off-list ref]
Subject: [PATCH 4/4] rtc: zynqmp: use dynamic max and min offset ranges

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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 <redacted>
---
 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

3bc8831ba2c4c4c701a49506b67ae6174f3ade3d..0cebc99b15a6de2440a60afc
2bd1769eccfa84b3 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)

        /* ticks to reach RTC_PPB */
        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))

The check 'freq + max_tick < 1' should be '<2' to prevent writing 0 to the calibration register when fract_offset < 0 causes max_tick--.
Example: freq=32767, max_tick=-32766 passes (sum=1), but after decrement becomes calibval=0.

calibval=0 is not documented as invalid calibration value. AFAIS it
would mean a frequency of 1Hz. Can You provide more info on this?

Thanks,
Tomas

quoted

+               return -ERANGE;
+
        /* Number fractional ticks for given offset */
        if (fract_offset) {
                /* round up here so we stay below a full tick */

--
2.47.3

Thanks,
Harini T