From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: Akashdeep Kaur <a-kaur@ti.com>
Cc: praneeth@ti.com, nm@ti.com, vigneshr@ti.com,
linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org,
sebin.francis@ti.com, s-tripathi1@ti.com, vishalm@ti.com,
k-willis@ti.com
Subject: Re: [PATCH 0/2] rtc: Prevent hctosys from using invalid RTC time
Date: Wed, 21 Oct 2026 09:13:51 +0200 [thread overview]
Message-ID: <202610210713515313f800@mail.local> (raw)
In-Reply-To: <20261021042435.3895543-1-a-kaur@ti.com>
Hello,
On 21/10/2026 09:54:33+0530, Akashdeep Kaur wrote:
> The kernel's boot-time RTC synchronization blindly trusts the RTC
> value when setting system time, but RTCs may have invalid time
> depending on the boot path:
>
> - On first cold boot: RTC may have lost power, time is invalid
> - After low-power mode (RTC-only) cold boot: RTC retained power, time
> is valid
>
> On normal cold boot where bootloader or NTP has already established
> correct time, boot-time sync (triggered when RTC driver loads as
> module or probes at boot) can overwrite it with invalid RTC data,
> causing time rollback to 1970. However, on boot from RTC-only power
> mode, the RTC has valid time and boot-time sync should work to
> restore system time from RTC.
>
> This series adds a flag that drivers set dynamically per-boot to
> indicate whether RTC has valid time. Drivers check at probe if RTC
> retained power through this specific boot. Boot-time sync checks this
> flag before setting system time. This enables correct behavior for
> both boot paths while keeping PM suspend/resume compensation
> unaffected.
The proper way to do this is to return -EINVAL in read_time until you
know the date is correct. There is no need for an extra flag for the core.
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
prev parent reply other threads:[~2026-10-21 7:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 4:24 Akashdeep Kaur
2026-10-21 4:24 ` [PATCH 1/2] rtc: Add flag for dynamic hctosys control Akashdeep Kaur
2026-10-21 4:24 ` [PATCH 2/2] rtc: ti-k3: Mark RTC time as invalid without battery backup Akashdeep Kaur
2026-10-21 7:13 ` Alexandre Belloni [this message]
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