Re: [PATCH v3] rtc: efi: restore alarm support with runtime capability probe

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Zero-initializing `eft` causes `efi_read_alarm()` to always fail with `-EIO` for disabled alarms, completely breaking userspace reads.
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commit b695e617f63e29889d5f34a76788ecbfdea7f619
Author: Johnny.Fan <Johnny.Fan@cixtech.com>

rtc: efi: restore alarm support with runtime capability probe

This commit restores EFI RTC alarm functionality removed in a previous commit.
It adds a capability probe at ->probe() time to check if GetWakeupTime()
actually works before exposing the alarm feature to the OS.

> diff --git a/drivers/rtc/rtc-efi.c b/drivers/rtc/rtc-efi.c
> index b4f44999ef0f4..a8c18ebc55996 100644
> --- a/drivers/rtc/rtc-efi.c
> +++ b/drivers/rtc/rtc-efi.c
[ ... ]
> @@ -112,6 +113,35 @@ convert_from_efi_time(efi_time_t *eft, struct rtc_time *wtime)
>  	return true;
>  }
>  
> +static int efi_read_alarm(struct device *dev, struct rtc_wkalrm *wkalrm)
> +{
> +	efi_time_t eft;
> +	efi_status_t status;
> +
> +	memset(&eft, 0, sizeof(eft));
> +	status = efi.get_wakeup_time((efi_bool_t *)&wkalrm->enabled,
> +				     (efi_bool_t *)&wkalrm->pending, &eft);
> +	if (status != EFI_SUCCESS)
> +		return -EINVAL;
> +
> +	if (!convert_from_efi_time(&eft, &wkalrm->time))
> +		return -EIO;

[Severity: High]
Does this zero-initialization cause efi_read_alarm() to fail unconditionally
with -EIO for disabled alarms?

When the alarm is disabled, firmware can return EFI_SUCCESS but leave the
eft structure untouched, as allowed by the UEFI spec. Because this patch adds
memset(&eft, 0, sizeof(eft)), eft.day and eft.month will remain 0.

Looking at convert_from_efi_time(), there is a preexisting validation check:

drivers/rtc/rtc-efi.c:convert_from_efi_time() {
    ...
	if (!eft->day || eft->day > 31)
		return false;
    ...
}

This check strictly rejects 0 as a valid day, nullifying the attempt to use
an all-zero structure to bypass validation. As a result, reading a disabled
RTC alarm will fail with -EIO rather than correctly reporting the disabled
state, breaking userspace tools like hwclock or sysfs reads that expect to
read the alarm status without a hard I/O error.

> +
> +	return rtc_valid_tm(&wkalrm->time);
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260831140014.839222-1-johnny.fan@cixtech.com?part=1