Re: [PATCH] x86/init: Initialize wall clock in get_rtc_noop()

[Naman Jain]

On 9/12/2026 9:05 AM, Roman Kisel wrote:
On Mon, Aug 31, 2026 at 08:25:28AM +0000, Naman Jain wrote:
get_rtc_noop() is used when an RTC is unavailable, but leaves its output
argument untouched. When CONFIG_INIT_STACK_ALL_ZERO is not enabled,
timekeeping_init() may therefore receive a nonzero invalid persistent
clock value and warn:
"Persistent clock returned invalid value"

Initialize the output to zero, the documented representation of an
unsupported persistent clock.

Fixes: c311ed6183f4 ("x86/init: Allow DT configured systems to disable RTC at boot 
time")
Cc: sta...@vger.kernel.org
Signed-off-by: Naman Jain <namj...@linux.microsoft.com>
---
  arch/x86/kernel/x86_init.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index 252c5827d0634..3b9b41820c84c 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -37,7 +37,7 @@ static void iommu_shutdown_noop(void) { }
  bool __init bool_x86_init_noop(void) { return false; }
  void x86_op_int_noop(int cpu) { }
  int set_rtc_noop(const struct timespec64 *now) { return -EINVAL; }
-void get_rtc_noop(struct timespec64 *now) { }
+void get_rtc_noop(struct timespec64 *now) { *now = (struct timespec64){0}; }

Hi Naman,

Could be

*now = (struct timespec64){};

to save a byte :)

hi Roman,
Thanks for reviewing.

Tianyu pointed out offline that this is handled in yet another way in 
jailhouse code:

arch/x86/kernel/jailhouse.c
static void jailhouse_get_wallclock(struct timespec64 *now)
{
      memset(now, 0, sizeof(now));
}

Regards,
Naman


LGTM.
Reviewed-by: Roman Kisel <v...@mailbox.org>

  
  static __initconst const struct of_device_id of_cmos_match[] = {
        { .compatible = "motorola,mc146818" },
--
2.43.0