RE: [PATCH 2/4] rtc: zynqmp: rework read_offset
From: T, Harini <hidden>
Date: 2025-12-09 17:28:50
Also in:
linux-rtc, lkml
[Public] Hi,
quoted hunk ↗ jump to hunk
-----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 2/4] rtc: zynqmp: rework read_offset Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding. read_offset() was using static frequency for determining the tick offset. It was also using remainder from do_div() operation as tick_mult value which caused the offset to be incorrect. At the same time, rework function to improve readability. Signed-off-by: Tomas Melin <redacted> --- drivers/rtc/rtc-zynqmp.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-)diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c index856bc1678e7d31144f320ae9f75fc58c742a2a64..7af5f6f99538f961a53ff56bfc6 56c907611b900 100644--- a/drivers/rtc/rtc-zynqmp.c +++ b/drivers/rtc/rtc-zynqmp.c@@ -178,21 +178,28 @@ static void xlnx_init_rtc(struct xlnx_rtc_dev*xrtcdev) static int xlnx_rtc_read_offset(struct device *dev, long *offset) { struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev); - unsigned long long rtc_ppb = RTC_PPB; - unsigned int tick_mult = do_div(rtc_ppb, xrtcdev->freq); - unsigned int calibval; + unsigned int calibval, fract_data, fract_part;
Prefer one variable assignment per line for readability.
+ int max_tick, tick_mult;
It would be better to explain why tick_mult is changed to int in the commit message.
+ int freq = xrtcdev->freq;
Please follow reverse xmas tree variable ordering.
long offset_val; + /* ticks to reach RTC_PPB */
The comment is misleading. Its tick_mult is nanoseconds per tick, not a tick count.
+ tick_mult = DIV_ROUND_CLOSEST(RTC_PPB, freq);
+
calibval = readl(xrtcdev->reg_base + RTC_CALIB_RD);
/* Offset with seconds ticks */
- offset_val = calibval & RTC_TICK_MASK;
- offset_val = offset_val - RTC_CALIB_DEF;
- offset_val = offset_val * tick_mult;
+ max_tick = calibval & RTC_TICK_MASK;
+ offset_val = max_tick - freq;
+ /* Convert to ppb */
+ offset_val *= tick_mult;
/* Offset with fractional ticks */
- if (calibval & RTC_FR_EN)
- offset_val += ((calibval & RTC_FR_MASK) >> RTC_FR_DATSHIFT)
- * (tick_mult / RTC_FR_MAX_TICKS);
+ if (calibval & RTC_FR_EN) {
+ fract_data = (calibval & RTC_FR_MASK) >> RTC_FR_DATSHIFT;
+ fract_part = DIV_ROUND_UP(tick_mult, RTC_FR_MAX_TICKS);
+ offset_val += (fract_part * fract_data);
+ }
+
*offset = offset_val;
return 0;
--
2.47.3Regards, Harini T