linux-kernel - Re: [PATCH v2] rtc: efi: Defer driver initialization to prioritize more capable RTCs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAAhV-H5Kq0Dnyt_w7iN_cB6ai8f_8V5Sot7m7zTC+UxeF15pxg@mail.gmail.com>
Date: Tue, 17 Jun 2025 22:17:25 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Ming Wang <wangming01@...ngson.cn>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>, linux-rtc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, lixuefeng@...ngson.cn, chenhuacai@...ngson.cn, 
	gaojuxin@...ngson.cn
Subject: Re: [PATCH v2] rtc: efi: Defer driver initialization to prioritize
 more capable RTCs

On Fri, Jun 13, 2025 at 2:18 PM Ming Wang <wangming01@...ngson.cn> wrote:
>
> The EFI GetWakeupTime call, used by efi_read_alarm() to fetch RTC
> wakeup alarm information, is specified to return EFI_UNSUPPORTED on
> EFI firmware v1.10 and later. This effectively means that on most
> modern systems, the efi-rtc driver cannot provide working RTC alarm
> functionality.
>
> If efi-rtc registers early during boot, it might become the primary
> RTC device (e.g., /dev/rtc0). This can lead to a situation where the
> system appears to have an RTC, but userspace utilities cannot set or
> get RTC alarms, even if other RTC hardware (like rtc-cmos, which
> typically supports alarms) is present but registers later.
>
> To address this, change the efi-rtc driver initialization from
> module_init() to late_initcall(). By deferring its initialization,
> we give other, potentially more capable RTC drivers (such as rtc-cmos)
> a better chance to register first and become the primary RTC.
>
> This change increases the likelihood that systems with multiple RTC
> sources will use the one with the most complete feature set (including
> alarms) as the primary RTC. The efi-rtc driver can still serve as a
> time source or a fallback RTC if no other RTC is available or preferred.
This makes sense because platform-specific RTCs usually have richer
features (so preferable) than EFI-RTC, and some test programs (such as
LTP) only operate on /dev/rtc0.

Reviewed-by: Huacai Chen <chenhuacai@...ngson.cn>

>
> Signed-off-by: Ming Wang <wangming01@...ngson.cn>
> ---
> Changes in v2:
> - Fixed a section mismatch warning reported by the kernel test robot.
>   The efi_rtc_probe function was previously marked __init, which
>   caused a conflict when efi_rtc_driver (in .data) directly
>   referenced it after its initialization was deferred. Removed the
>   __init attribute from efi_rtc_probe to resolve this.
> ---
>  drivers/rtc/rtc-efi.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-efi.c b/drivers/rtc/rtc-efi.c
> index fa8bf82df948..c941f52ea3fe 100644
> --- a/drivers/rtc/rtc-efi.c
> +++ b/drivers/rtc/rtc-efi.c
> @@ -254,7 +254,7 @@ static const struct rtc_class_ops efi_rtc_ops = {
>         .proc           = efi_procfs,
>  };
>
> -static int __init efi_rtc_probe(struct platform_device *dev)
> +static int efi_rtc_probe(struct platform_device *dev)
>  {
>         struct rtc_device *rtc;
>         efi_time_t eft;
> @@ -286,9 +286,20 @@ static struct platform_driver efi_rtc_driver = {
>         .driver = {
>                 .name = "rtc-efi",
>         },
> +       .probe = efi_rtc_probe,
>  };
>
> -module_platform_driver_probe(efi_rtc_driver, efi_rtc_probe);
> +static int __init efi_rtc_driver_init(void)
> +{
> +       return platform_driver_register(&efi_rtc_driver);
> +}
> +late_initcall(efi_rtc_driver_init);
> +
> +static void __exit efi_rtc_driver_exit(void)
> +{
> +       platform_driver_unregister(&efi_rtc_driver);
> +}
> +module_exit(efi_rtc_driver_exit);
>
>  MODULE_AUTHOR("dann frazier <dannf@...nf.org>");
>  MODULE_LICENSE("GPL");
> --
> 2.43.0
>