linux-kernel - Re: [PATCH 4/7] rtc: pm8xxx: mitigate flash wear

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Message-ID: <Z5IqZcRbd1vkyp-Z@hovoldconsulting.com>
Date: Thu, 23 Jan 2025 12:39:17 +0100
From: Johan Hovold <johan@...nel.org>
To: Johan Hovold <johan+linaro@...nel.org>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Jonathan Marek <jonathan@...ek.ca>, linux-arm-msm@...r.kernel.org,
	linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] rtc: pm8xxx: mitigate flash wear

On Mon, Jan 20, 2025 at 03:41:49PM +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.
> 
> On machines like the Lenovo ThinkPad X14s the PMIC RTC drifts about one

s/X14s/X13s/

> second every 3.5 hours, something which leads to repeated updates of the
> offset when NTP synchronisation is enabled.
> 
> Reduce wear of the underlying flash storage (used for UEFI variables) by
> deferring writes until shutdown in case they appear to be due to clock
> drift.
> 
> As an example, allowing the on-flash offset to differ up to 30 s reduces

And this was supposed to say:

	As an example, deferring writes when the new offset differs up
	to 30 s from the previous one reduces
	
> the number of writes on the X13s during a ten day session with the
> machine not suspending for more than four days in a row from up to 68
> writes (every 3.5 h) to at most two (boot and shutdown).

Johan