linux-kernel - Re: [PATCH v2 17/22] rtc: pm8xxx: add support for nvmem offset

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Message-ID: <Y9y2T+mrzDk5IVq9@hovoldconsulting.com>
Date:   Fri, 3 Feb 2023 08:22:55 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        linux-arm-msm@...r.kernel.org, linux-rtc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 17/22] rtc: pm8xxx: add support for nvmem offset

On Fri, Feb 03, 2023 at 04:31:54AM +0100, Konrad Dybcio wrote:
> 
> 
> On 2.02.2023 16:54, Johan Hovold wrote:
> > On many Qualcomm platforms the PMIC RTC control and time registers are
> > read-only so that the RTC time can not be updated. Instead an offset
> > needs be stored in some machine-specific non-volatile memory, which the
> > driver can take into account.
> > 
> > Add support for storing a 32-bit offset from the Epoch in an nvmem cell
> > so that the RTC time can be set on such platforms.
> > 
> > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> > ---
> That's gonna be a stupid question, but just to make sure..
> 
> SDAM is rewritable, right? So that when somebody sets the time to
> year 2077 by mistake, they won't have to put up with it for the next
> 50 years? :D

Heh, yes, it is re-writeable. Otherwise, using SDAM wouldn't really have
been an alternative to using the UEFI offset. :)

These registers are reset if you lose battery power so you'd be back at
1970 as expected if that ever happens too.

Johan