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From:   "Neeli, Srinivas" <srinivas.neeli@amd.com>
To:     Peter Korsgaard <peter@korsgaard.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>
CC:     Srinivas Neeli <srinivas.neeli@xilinx.com>,
        "a.zummo@towertech.it" <a.zummo@towertech.it>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "krzysztof.kozlowski+dt@linaro.org" 
        <krzysztof.kozlowski+dt@linaro.org>,
        "michal.simek@xilinx.com" <michal.simek@xilinx.com>,
        "sgoud@xilinx.com" <sgoud@xilinx.com>,
        "shubhraj@xilinx.com" <shubhraj@xilinx.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "git@xilinx.com" <git@xilinx.com>
Subject: RE: [PATCH V6 2/2] rtc: zynqmp: Add calibration set and get support
Thread-Topic: [PATCH V6 2/2] rtc: zynqmp: Add calibration set and get support
Thread-Index: AQHYfAq3H1AwUW9mCkuVxsTByCkLV61HKF6ZgAAA/QCAAAG6EYABPtcw
Date:   Fri, 10 Jun 2022 10:02:47 +0000
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[AMD Official Use Only - General]

Hi,

> -----Original Message-----
> From: Peter Korsgaard <peter@korsgaard.com>
> Sent: Thursday, June 9, 2022 8:30 PM
> To: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Cc: Srinivas Neeli <srinivas.neeli@xilinx.com>; a.zummo@towertech.it;
> robh+dt@kernel.org; krzysztof.kozlowski+dt@linaro.org;
> michal.simek@xilinx.com; sgoud@xilinx.com; shubhraj@xilinx.com; Neeli,
> Srinivas <srinivas.neeli@amd.com>; neelisrinivas18@gmail.com;
> devicetree@vger.kernel.org; linux-rtc@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; git@xilinx.com
> Subject: Re: [PATCH V6 2/2] rtc: zynqmp: Add calibration set and get supp=
ort
>
> >>>>> "Alexandre" =3D=3D Alexandre Belloni <alexandre.belloni@bootlin.com=
>
> writes:
>
>  > On 09/06/2022 16:50:03+0200, Peter Korsgaard wrote:
>  >> >>>>> "Srinivas" =3D=3D Srinivas Neeli <srinivas.neeli@xilinx.com> wr=
ites:
>  >>
>  >> > 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.
>  >> > As per RTC spec default calibration value is 0x7FFF.
>  >>
>  >> Where do you see that? ug1085 rev2.2 still lists:
>  >>
>  >> Programming Sequences
>  >> init rtc
>  >> 1. Write the value 0019_8231h into the calibration register, CALIB_WR=
ITE.
>  >>
>
>  > This is a very weird value. Last time I had a look, I couldn't find an=
  >
> explanation for it.
>
> Agreed. I am not arguing that it is sensible, I just wondered where this =
new
> value comes from?
>
This information is missing in our TRM, as per the internal RTC IP design s=
pecification document, the calibration value should be crystal clock freque=
ncy minus one.
For a crystal oscillator of 32.768KHz(0x8000) frequency, the calibration va=
lue will be 0x7FFF.

Will update TRM with the required information.

> --
> Bye, Peter Korsgaard