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

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Message-ID: <87mtel287y.fsf@dell.be.48ers.dk>
Date:   Thu, 09 Jun 2022 16:59:45 +0200
From:   Peter Korsgaard <peter@...sgaard.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.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

>>>>> "Alexandre" == Alexandre Belloni <alexandre.belloni@...tlin.com> writes:

 > 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.

Agreed. I am not arguing that it is sensible, I just wondered where this
new value comes from?

-- 
Bye, Peter Korsgaard