linux-kernel - Re: [RFC 18/24] dt-bindings: rtc: qcom-pm8xxx: add uefi-variable offset

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Message-ID: <20230130184944.GA3096050-robh@kernel.org>
Date:   Mon, 30 Jan 2023 12:49:44 -0600
From:   Rob Herring <robh@...nel.org>
To:     Johan Hovold <johan+linaro@...nel.org>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        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: [RFC 18/24] dt-bindings: rtc: qcom-pm8xxx: add uefi-variable
 offset

On Thu, Jan 26, 2023 at 03:20:51PM +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 a
> driver can take into account.
> 
> Add a 'qcom,uefi-rtc-info' boolean flag which indicates that the RTC
> offset is stored in a Qualcomm specific UEFI variable so that the RTC
> time can be updated on such platforms.
> 
> 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.

Can't you just try to read the UEFI variable and use it if that 
succeeds?

I don't like this in DT because what if lots of devices start storing 
lots of things in vendor specific UEFI variables. It doesn't scale.

Rob