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

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Message-ID: <Y9P0zuovXqBbFSLs@mail.local>
Date:   Fri, 27 Jan 2023 16:59:10 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Johan Hovold <johan@...nel.org>
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 27/01/2023 16:26:26+0100, Johan Hovold wrote:
> 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).

I expected this answer so please add this to the commit message, this
will be the fifth epoch we ave to handle then...

> 
> > > 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

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