linux-kernel - Re: [PATCH 19/24] rtc: pm8xxx: add support for uefi offset

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Message-ID: <Y9PtIiD1o8eBq2wk@hovoldconsulting.com>
Date:   Fri, 27 Jan 2023 16:26:26 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.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 19/24] rtc: pm8xxx: add support for uefi offset

On Fri, Jan 27, 2023 at 04:19:18PM +0100, Alexandre Belloni wrote:
> On 26/01/2023 15:20:52+0100, 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 GPS time epoch in a
> > UEFI variable so that the RTC time can be set on such platforms.
> > 
> 
> Why are you using the GPS epoch? This seems pretty random.

Tell that to the Qualcomm firmware team. ;)

Perhaps I could have made it more clear, but this is the format that the
firmware uses so Linux is not free to pick a different base here (or
time would differ ten years between UEFI/Windows and Linux).

> > The UEFI variable is
> > 
> >             882f8c2b-9646-435f-8de5-f208ff80c1bd-RTCInfo
> > 
> > and holds a 12-byte structure where the first four bytes is a GPS time
> > offset in little-endian byte order.

Johan