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

From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: Johan Hovold <johan@kernel.org>
Cc: Johan Hovold <johan+linaro@kernel.org>,
	Bjorn Andersson <andersson@kernel.org>,
	Andy Gross <agross@kernel.org>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Alessandro Zummo <a.zummo@towertech.it>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Maximilian Luz <luzmaximilian@gmail.com>,
	linux-arm-msm@vger.kernel.org, linux-rtc@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 19/24] rtc: pm8xxx: add support for uefi offset
Date: Fri, 27 Jan 2023 16:59:10 +0100	[thread overview]
Message-ID: <Y9P0zuovXqBbFSLs@mail.local> (raw)
In-Reply-To: <Y9PtIiD1o8eBq2wk@hovoldconsulting.com>

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