linux-kernel - Re: [PATCH V6 2/2] rtc: zynqmp: Add calibration set and get support

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Date:   Thu, 9 Jun 2022 16:53:46 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Peter Korsgaard <peter@...sgaard.com>
Cc:     Srinivas Neeli <srinivas.neeli@...inx.com>, a.zummo@...ertech.it,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        michal.simek@...inx.com, sgoud@...inx.com, shubhraj@...inx.com,
        srinivas.neeli@....com, neelisrinivas18@...il.com,
        devicetree@...r.kernel.org, linux-rtc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        git@...inx.com
Subject: Re: [PATCH V6 2/2] rtc: zynqmp: Add calibration set and get support

On 09/06/2022 16:50:03+0200, Peter Korsgaard wrote:
> >>>>> "Srinivas" == Srinivas Neeli <srinivas.neeli@...inx.com> writes:
> 
>  > 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_WRITE.
> 

This is a very weird value. Last time I had a look, I couldn't find an
explanation for it.

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com