linux-kernel - RE: [PATCH 4/4] rtc: zynqmp: use dynamic max and min offset ranges

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Message-ID:
 <LV5PR12MB98046A63E80D7A7FA299366E92A3A@LV5PR12MB9804.namprd12.prod.outlook.com>
Date: Tue, 9 Dec 2025 19:28:44 +0000
From: "T, Harini" <Harini.T@....com>
To: Tomas Melin <tomas.melin@...sala.com>, Alexandre Belloni
	<alexandre.belloni@...tlin.com>, "Simek, Michal" <michal.simek@....com>
CC: "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 4/4] rtc: zynqmp: use dynamic max and min offset ranges

[Public]

Hi,

> -----Original Message-----
> From: Tomas Melin <tomas.melin@...sala.com>
> Sent: Monday, December 1, 2025 6:20 PM
> To: Alexandre Belloni <alexandre.belloni@...tlin.com>; Simek, Michal
> <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 4/4] rtc: zynqmp: use dynamic max and min offset ranges
>
> Caution: This message originated from an External Source. Use proper
> caution when opening attachments, clicking links, or responding.
>
>
> 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
> 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.
> +               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