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Date:   Mon, 18 Oct 2021 09:55:08 +0000
From:   Srinivas Neeli <sneeli@...inx.com>
To:     Srinivas Neeli <sneeli@...inx.com>,
        "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        Michal Simek <michals@...inx.com>,
        Srinivas Goud <sgoud@...inx.com>,
        Shubhrajyoti Datta <shubhraj@...inx.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>,
        git <git@...inx.com>
Subject: RE: [PATCH V2] rtc: zynqmp: Add calibration set and get support

> -----Original Message-----
> From: Srinivas Neeli <srinivas.neeli@...inx.com>
> Sent: Monday, September 27, 2021 12:09 PM
> To: a.zummo@...ertech.it; alexandre.belloni@...tlin.com; Michal Simek
> <michals@...inx.com>; Srinivas Goud <sgoud@...inx.com>; Shubhrajyoti
> Datta <shubhraj@...inx.com>
> Cc: linux-rtc@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; git <git@...inx.com>; Srinivas Neeli
> <sneeli@...inx.com>
> Subject: [PATCH V2] rtc: zynqmp: Add calibration set and get support
> 
> Zynqmp RTC controller has a calibration feature to compensate time
> deviation due to input clock inaccuracy.
> Set and get calibration API's are used for setting and getting calibration value
> from the controller calibration register.
> 
> Signed-off-by: Srinivas Neeli <srinivas.neeli@...inx.com>
> ---
> Changes in V2:
> -Removed unused macro.
> -Updated code with review comments.
> ---
>  drivers/rtc/rtc-zynqmp.c | 100 ++++++++++++++++++++++++++++++++----
> ---

Hi alexandre,
Could you please comment on this patch.

Thanks
Srinivas Neeli


>  1 file changed, 83 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c index
> f440bb52be92..3731ddfbd90f 100644
> --- a/drivers/rtc/rtc-zynqmp.c
> +++ b/drivers/rtc/rtc-zynqmp.c
> @@ -36,10 +36,15 @@
>  #define RTC_OSC_EN		BIT(24)
>  #define RTC_BATT_EN		BIT(31)
> 
> -#define RTC_CALIB_DEF		0x198233
> +#define RTC_CALIB_DEF		0x8000
>  #define RTC_CALIB_MASK		0x1FFFFF
>  #define RTC_ALRM_MASK          BIT(1)
>  #define RTC_MSEC               1000
> +#define RTC_FR_MASK		0xF0000
> +#define RTC_FR_MAX_TICKS	16
> +#define RTC_OFFSET_MAX		150000
> +#define RTC_OFFSET_MIN		-150000
> +#define RTC_PPB			1000000000LL
> 
>  struct xlnx_rtc_dev {
>  	struct rtc_device	*rtc;
> @@ -61,13 +66,6 @@ static int xlnx_rtc_set_time(struct device *dev, struct
> rtc_time *tm)
>  	 */
>  	new_time = rtc_tm_to_time64(tm) + 1;
> 
> -	/*
> -	 * Writing into calibration register will clear the Tick Counter and
> -	 * force the next second to be signaled exactly in 1 second period
> -	 */
> -	xrtcdev->calibval &= RTC_CALIB_MASK;
> -	writel(xrtcdev->calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
> -
>  	writel(new_time, xrtcdev->reg_base + RTC_SET_TM_WR);
> 
>  	/*
> @@ -174,14 +172,76 @@ static void xlnx_init_rtc(struct xlnx_rtc_dev
> *xrtcdev)
>  	rtc_ctrl |= RTC_BATT_EN;
>  	writel(rtc_ctrl, xrtcdev->reg_base + RTC_CTRL);
> 
> -	/*
> -	 * Based on crystal freq of 33.330 KHz
> -	 * set the seconds counter and enable, set fractions counter
> -	 * to default value suggested as per design spec
> -	 * to correct RTC delay in frequency over period of time.
> +	/* Update calibvalue */
> +	xrtcdev->calibval = readl(xrtcdev->reg_base + RTC_CALIB_RD); }
> +
> +static int xlnx_rtc_read_offset(struct device *dev, long *offset) {
> +	struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev);
> +	long offset_val = 0;
> +	unsigned int tick_mult = RTC_PPB / (xrtcdev->calibval &
> +RTC_TICK_MASK);
> +
> +	/* Offset with seconds ticks */
> +	offset_val = xrtcdev->calibval & RTC_TICK_MASK;
> +	offset_val = offset_val - RTC_CALIB_DEF;
> +	offset_val = offset_val * tick_mult;
> +
> +	/* Offset with fractional ticks */
> +	if (xrtcdev->calibval & RTC_FR_EN)
> +		offset_val += ((xrtcdev->calibval & RTC_FR_MASK) >>
> RTC_FR_DATSHIFT)
> +			* (tick_mult / RTC_FR_MAX_TICKS);
> +	*offset = offset_val;
> +
> +	return 0;
> +}
> +
> +static int xlnx_rtc_set_offset(struct device *dev, long offset) {
> +	struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev);
> +	short int  max_tick;
> +	unsigned char fract_tick = 0;
> +	unsigned int calibval;
> +	int fract_offset;
> +	unsigned int tick_mult = RTC_PPB / (xrtcdev->calibval &
> +RTC_TICK_MASK);
> +
> +	/* Make sure offset value is within supported range */
> +	if (offset < RTC_OFFSET_MIN || offset > RTC_OFFSET_MAX)
> +		return -ERANGE;
> +
> +	/* Number ticks for given offset */
> +	max_tick = div_s64_rem(offset, tick_mult, &fract_offset);
> +
> +	/* Number fractional ticks for given offset */
> +	if (fract_offset) {
> +		if (fract_offset < 0) {
> +			fract_offset = fract_offset + tick_mult;
> +			max_tick--;
> +		}
> +		if (fract_offset > (tick_mult / RTC_FR_MAX_TICKS)) {
> +			for (fract_tick = 1; fract_tick < 16; fract_tick++) {
> +				if (fract_offset <=
> +				    (fract_tick *
> +				     (tick_mult / RTC_FR_MAX_TICKS)))
> +					break;
> +			}
> +		}
> +	}
> +
> +	/* Zynqmp RTC uses second and fractional tick
> +	 * counters for compensation
>  	 */
> -	xrtcdev->calibval &= RTC_CALIB_MASK;
> -	writel(xrtcdev->calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
> +	calibval = max_tick + RTC_CALIB_DEF;
> +
> +	if (fract_tick)
> +		calibval |= RTC_FR_EN;
> +
> +	calibval |= (fract_tick << RTC_FR_DATSHIFT);
> +
> +	writel(calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
> +	xrtcdev->calibval = calibval;
> +
> +	return 0;
>  }
> 
>  static const struct rtc_class_ops xlnx_rtc_ops = { @@ -190,6 +250,8 @@
> static const struct rtc_class_ops xlnx_rtc_ops = {
>  	.read_alarm	  = xlnx_rtc_read_alarm,
>  	.set_alarm	  = xlnx_rtc_set_alarm,
>  	.alarm_irq_enable = xlnx_rtc_alarm_irq_enable,
> +	.read_offset	  = xlnx_rtc_read_offset,
> +	.set_offset	  = xlnx_rtc_set_offset,
>  };
> 
>  static irqreturn_t xlnx_rtc_interrupt(int irq, void *id) @@ -215,6 +277,7 @@
> static int xlnx_rtc_probe(struct platform_device *pdev)  {
>  	struct xlnx_rtc_dev *xrtcdev;
>  	int ret;
> +	unsigned int calibval;
> 
>  	xrtcdev = devm_kzalloc(&pdev->dev, sizeof(*xrtcdev),
> GFP_KERNEL);
>  	if (!xrtcdev)
> @@ -256,9 +319,12 @@ static int xlnx_rtc_probe(struct platform_device
> *pdev)
>  	}
> 
>  	ret = of_property_read_u32(pdev->dev.of_node, "calibration",
> -				   &xrtcdev->calibval);
> +				   &calibval);
>  	if (ret)
> -		xrtcdev->calibval = RTC_CALIB_DEF;
> +		calibval = RTC_CALIB_DEF;
> +	ret = readl(xrtcdev->reg_base + RTC_CALIB_RD);
> +	if (!ret)
> +		writel(calibval, (xrtcdev->reg_base + RTC_CALIB_WR));
> 
>  	xlnx_init_rtc(xrtcdev);
> 
> --
> 2.17.1

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