linux-kernel - Re: [PATCH v4 0/5] rtc: zynqmp: fixes for read and set offset

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Message-ID: <739e70b2-b4d1-457a-9f00-d19766f0ef76@amd.com>
Date: Thu, 29 Jan 2026 11:11:52 +0100
From: Michal Simek <michal.simek@....com>
To: Tomas Melin <tomas.melin@...sala.com>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: linux-rtc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Harini T <harini.t@....com>
Subject: Re: [PATCH v4 0/5] rtc: zynqmp: fixes for read and set offset



On 1/22/26 14:53, Tomas Melin wrote:
> Add improvements for read and set offset functions.
> The basic functionality is still the same, but offset correction values
> are now updated to match with expected.
> 
> The RTC calibration value operates with full ticks,
> and fractional ticks which are a 1/16 of a full tick.
> The 16 lowest bits in the calibration registers are for the full ticks
> and value matches the external oscillator in Hz. Through that,
> the maximum and minimum offset values can be calculated dynamically,
> as they depend on the input frequency used.
> 
> For docs on the calibration register, see
> https://docs.amd.com/r/en-US/ug1087-zynq-ultrascale-registers/CALIB_READ-RTC-Register
> 
> Due to rounding errors (different number of fract ticks),
> offset readback will differ slightly depending on
> if the offset is negative or positive. This is however well below the granularity
> provided by the hardware.
> 
> For example
> $ echo 34335 > offset
> $ cat offset
> 34335
> $ echo -34335 > offset
> $ cat offset
> -34326
> 
> Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
> ---
> Changes in v4:
> - Do not limit building to zynqmp arch as building on other platforms
>    might be needed. Implies dropping commit.
> - No need for RTC_PPB to be 64 bit value, use 32 bit instead
> - Link to v3: https://lore.kernel.org/r/20260119-zynqmp-rtc-updates-v3-0-acd902fdeab1@vaisala.com
> 
> Changes in v3:
> - Add commit for limiting building of driver to zynqmp arch.
> - Reorder variable declarations in set_offset
> - Link to v2: https://lore.kernel.org/r/20260108-zynqmp-rtc-updates-v2-0-864c161fa83d@vaisala.com
> 
> Changes in v2:
> - Add commit introducing check for calibration value overflow
> - Update comments
> - Align data types across set and read
> - Rename fract_tick as fract_data conforming to data sheet
> - Further improve on set offset calculation logic
> - Link to v1: https://lore.kernel.org/r/20251201-zynqmp-rtc-updates-v1-0-33875c1e385b@vaisala.com
> 
> ---
> Tomas Melin (5):
>        rtc: zynqmp: correct frequency value
>        rtc: zynqmp: check calibration max value
>        rtc: zynqmp: rework read_offset
>        rtc: zynqmp: rework set_offset
>        rtc: zynqmp: use dynamic max and min offset ranges
> 
>   drivers/rtc/rtc-zynqmp.c | 75 ++++++++++++++++++++++++++----------------------
>   1 file changed, 41 insertions(+), 34 deletions(-)
> ---
> base-commit: cd635e33b0113287c94021be53d2a7c61a1614e9
> change-id: 20251201-zynqmp-rtc-updates-d260364cc01b
> 
> Best regards,

Acked-by: Michal Simek <michal.simek@....com>

Thanks,
Michal