[PATCH v4 4/6] x86/time: introduce probing logic for the wallclock

Roger Pau Monne posted 6 patches 3 months ago
There is a newer version of this series
[PATCH v4 4/6] x86/time: introduce probing logic for the wallclock
Posted by Roger Pau Monne 3 months ago
Adding such probing allows to clearly separate init vs runtime code, and to
place the probing logic into the init section for the CMOS case.  Note both
the Xen shared_info page wallclock, and the EFI wallclock don't really have any
probing-specific logic.  The shared_info wallclock will always be there if
booted as a Xen guest, while the EFI_GET_TIME method probing relies on checking
if it returns a value different than 0.

The panic message printed when Xen is unable to find a viable wallclock source
has been adjusted slightly, I believe the printed guidance still provides the
same amount of information to the user.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Changes since v3:
 - Remove ASSERT from cmos_read().
 - Change indentation of panic message arguments in probe_wallclock().
 - Add __init attribute.

Changes since v2:
 - New in this version.
---
 xen/arch/x86/time.c | 118 +++++++++++++++++++++++++++++++++++---------
 1 file changed, 94 insertions(+), 24 deletions(-)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 1e3c13fc7360..9ebeee61b987 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -1291,14 +1291,23 @@ static bool __get_cmos_time(struct rtc_time *rtc)
     return t1 <= SECONDS(1) && t2 < MILLISECS(3);
 }
 
-static bool cmos_probe(struct rtc_time *rtc_p, bool cmos_rtc_probe)
+static bool __initdata cmos_rtc_probe;
+boolean_param("cmos-rtc-probe", cmos_rtc_probe);
+
+static bool __init cmos_probe(void)
 {
     unsigned int seconds = 60;
 
+    if ( !(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) )
+        return true;
+
+    if ( !cmos_rtc_probe )
+        return false;
+
     for ( ; ; )
     {
-        bool success = __get_cmos_time(rtc_p);
-        struct rtc_time rtc = *rtc_p;
+        struct rtc_time rtc;
+        bool success = __get_cmos_time(&rtc);
 
         if ( likely(!cmos_rtc_probe) )
             return true;
@@ -1328,28 +1337,12 @@ static bool cmos_probe(struct rtc_time *rtc_p, bool cmos_rtc_probe)
     return false;
 }
 
-static unsigned long get_cmos_time(void)
+
+static unsigned long cmos_read(void)
 {
-    unsigned long res;
     struct rtc_time rtc;
-    static bool __read_mostly cmos_rtc_probe;
-    boolean_param("cmos-rtc-probe", cmos_rtc_probe);
 
-    if ( efi_enabled(EFI_RS) )
-    {
-        res = efi_get_time();
-        if ( res )
-            return res;
-    }
-
-    if ( likely(!(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC)) )
-        cmos_rtc_probe = false;
-    else if ( system_state < SYS_STATE_smp_boot && !cmos_rtc_probe )
-        panic("System with no CMOS RTC advertised must be booted from EFI"
-              " (or with command line option \"cmos-rtc-probe\")\n");
-
-    if ( !cmos_probe(&rtc, cmos_rtc_probe) )
-        panic("No CMOS RTC found - system must be booted from EFI\n");
+    __get_cmos_time(&rtc);
 
     return mktime(rtc.year, rtc.mon, rtc.day, rtc.hour, rtc.min, rtc.sec);
 }
@@ -1532,12 +1525,85 @@ void rtc_guest_write(unsigned int port, unsigned int data)
     }
 }
 
-static unsigned long get_wallclock_time(void)
+static enum {
+    WALLCLOCK_UNSET,
+    WALLCLOCK_XEN,
+    WALLCLOCK_CMOS,
+    WALLCLOCK_EFI,
+} wallclock_source __ro_after_init;
+
+static const char *__init wallclock_type_to_string(void)
 {
+    switch ( wallclock_source )
+    {
+    case WALLCLOCK_XEN:
+        return "XEN";
+
+    case WALLCLOCK_CMOS:
+        return "CMOS RTC";
+
+    case WALLCLOCK_EFI:
+        return "EFI";
+
+    case WALLCLOCK_UNSET:
+        return "UNSET";
+    }
+
+    ASSERT_UNREACHABLE();
+    return "";
+}
+
+static void __init probe_wallclock(void)
+{
+    ASSERT(wallclock_source == WALLCLOCK_UNSET);
+
     if ( xen_guest )
+    {
+        wallclock_source = WALLCLOCK_XEN;
+        return;
+    }
+    if ( efi_enabled(EFI_RS) && efi_get_time() )
+    {
+        wallclock_source = WALLCLOCK_EFI;
+        return;
+    }
+    if ( cmos_probe() )
+    {
+        wallclock_source = WALLCLOCK_CMOS;
+        return;
+    }
+
+    panic("No usable wallclock found, probed:%s%s%s\n%s",
+          !cmos_rtc_probe && !efi_enabled(EFI_RS) ? " None" : "",
+          cmos_rtc_probe ? " CMOS" : "",
+          efi_enabled(EFI_RS) ? " EFI" : "",
+          !cmos_rtc_probe
+              ? "Try with command line option \"cmos-rtc-probe\"\n"
+              : !efi_enabled(EFI_RS)
+                  ? "System must be booted from EFI\n"
+                  : "");
+}
+
+static unsigned long get_wallclock_time(void)
+{
+    switch ( wallclock_source )
+    {
+    case WALLCLOCK_XEN:
         return read_xen_wallclock();
 
-    return get_cmos_time();
+    case WALLCLOCK_CMOS:
+        return cmos_read();
+
+    case WALLCLOCK_EFI:
+        return efi_get_time();
+
+    case WALLCLOCK_UNSET:
+        /* Unexpected state - handled by the ASSERT_UNREACHABLE() below. */
+        break;
+    }
+
+    ASSERT_UNREACHABLE();
+    return 0;
 }
 
 /***************************************************************************
@@ -2462,6 +2528,10 @@ int __init init_xen_time(void)
 
     open_softirq(TIME_CALIBRATE_SOFTIRQ, local_time_calibration);
 
+    probe_wallclock();
+
+    printk(XENLOG_INFO "Wallclock source: %s\n", wallclock_type_to_string());
+
     /* NB. get_wallclock_time() can take over one second to execute. */
     do_settime(get_wallclock_time(), 0, NOW());
 
-- 
2.46.0


Re: [PATCH v4 4/6] x86/time: introduce probing logic for the wallclock
Posted by Jan Beulich 2 months, 4 weeks ago
On 04.09.2024 17:31, Roger Pau Monne wrote:
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -1291,14 +1291,23 @@ static bool __get_cmos_time(struct rtc_time *rtc)
>      return t1 <= SECONDS(1) && t2 < MILLISECS(3);
>  }
>  
> -static bool cmos_probe(struct rtc_time *rtc_p, bool cmos_rtc_probe)
> +static bool __initdata cmos_rtc_probe;
> +boolean_param("cmos-rtc-probe", cmos_rtc_probe);
> +
> +static bool __init cmos_probe(void)

I'm sorry for not paying attention to this earlier, but "cmos" alone
is misleading here and perhaps even more so for cmos_read(). These
aren't about the CMOS (storage) but the CMOS RTC. May I suggest
cmos_rtc_{probe,read}() instead?

>  {
>      unsigned int seconds = 60;
>  
> +    if ( !(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) )
> +        return true;
> +
> +    if ( !cmos_rtc_probe )
> +        return false;

With this I think ...

>      for ( ; ; )
>      {
> -        bool success = __get_cmos_time(rtc_p);
> -        struct rtc_time rtc = *rtc_p;
> +        struct rtc_time rtc;
> +        bool success = __get_cmos_time(&rtc);
>  
>          if ( likely(!cmos_rtc_probe) )
>              return true;

... this ends up being dead code.

Jan
Re: [PATCH v4 4/6] x86/time: introduce probing logic for the wallclock
Posted by Roger Pau Monné 2 months, 3 weeks ago
On Thu, Sep 05, 2024 at 05:58:47PM +0200, Jan Beulich wrote:
> On 04.09.2024 17:31, Roger Pau Monne wrote:
> > --- a/xen/arch/x86/time.c
> > +++ b/xen/arch/x86/time.c
> > @@ -1291,14 +1291,23 @@ static bool __get_cmos_time(struct rtc_time *rtc)
> >      return t1 <= SECONDS(1) && t2 < MILLISECS(3);
> >  }
> >  
> > -static bool cmos_probe(struct rtc_time *rtc_p, bool cmos_rtc_probe)
> > +static bool __initdata cmos_rtc_probe;
> > +boolean_param("cmos-rtc-probe", cmos_rtc_probe);
> > +
> > +static bool __init cmos_probe(void)
> 
> I'm sorry for not paying attention to this earlier, but "cmos" alone
> is misleading here and perhaps even more so for cmos_read(). These
> aren't about the CMOS (storage) but the CMOS RTC. May I suggest
> cmos_rtc_{probe,read}() instead?

I've assumed that those living in time.c would be clear enough it's
the CMOS RTC, but I'm fine with renaming to cmos_rtc_{probe,read}().

> 
> >  {
> >      unsigned int seconds = 60;
> >  
> > +    if ( !(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) )
> > +        return true;
> > +
> > +    if ( !cmos_rtc_probe )
> > +        return false;
> 
> With this I think ...
> 
> >      for ( ; ; )
> >      {
> > -        bool success = __get_cmos_time(rtc_p);
> > -        struct rtc_time rtc = *rtc_p;
> > +        struct rtc_time rtc;
> > +        bool success = __get_cmos_time(&rtc);
> >  
> >          if ( likely(!cmos_rtc_probe) )
> >              return true;
> 
> ... this ends up being dead code.

Indeed, I've missed to remove that one when moving the check outside
of the for loop.

Thanks, Roger.