[xen staging] x86/time: introduce probing logic for the wallclock

[patchbot@xxxxxxx]

commit cb4f22884e77c6bcfaa5f4be984b62106ea7c0d4
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Wed Sep 11 12:53:17 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Sep 11 12:53:17 2024 +0200

    x86/time: introduce probing logic for the wallclock
    
    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/time.c | 118 ++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 92 insertions(+), 26 deletions(-)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index ec48805a22..1dcbd9f520 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -1291,20 +1291,23 @@ static bool __get_cmos_time(struct rtc_time *rtc)
     return t1 <= SECONDS(1) && t2 < MILLISECS(3);
 }
 
-static bool __read_mostly opt_cmos_rtc_probe;
+static bool __initdata opt_cmos_rtc_probe;
 boolean_param("cmos-rtc-probe", opt_cmos_rtc_probe);
 
-static bool cmos_rtc_probe(struct rtc_time *rtc_p)
+static bool __init cmos_rtc_probe(void)
 {
     unsigned int seconds = 60;
 
+    if ( !(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) )
+        return true;
+
+    if ( !opt_cmos_rtc_probe )
+        return false;
+
     for ( ; ; )
     {
-        bool success = __get_cmos_time(rtc_p);
-        struct rtc_time rtc = *rtc_p;
-
-        if ( likely(!opt_cmos_rtc_probe) )
-            return true;
+        struct rtc_time rtc;
+        bool success = __get_cmos_time(&rtc);
 
         if ( !success ||
              rtc.sec >= 60 || rtc.min >= 60 || rtc.hour >= 24 ||
@@ -1331,26 +1334,12 @@ static bool cmos_rtc_probe(struct rtc_time *rtc_p)
     return false;
 }
 
-static unsigned long get_cmos_time(void)
+
+static unsigned long cmos_rtc_read(void)
 {
-    unsigned long res;
     struct rtc_time rtc;
 
-    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)) )
-        opt_cmos_rtc_probe = false;
-    else if ( system_state < SYS_STATE_smp_boot && !opt_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_rtc_probe(&rtc) )
-        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);
 }
@@ -1533,12 +1522,85 @@ 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_rtc_probe() )
+    {
+        wallclock_source = WALLCLOCK_CMOS;
+        return;
+    }
+
+    panic("No usable wallclock found, probed:%s%s%s\n%s",
+          !opt_cmos_rtc_probe && !efi_enabled(EFI_RS) ? " None" : "",
+          opt_cmos_rtc_probe ? " CMOS" : "",
+          efi_enabled(EFI_RS) ? " EFI" : "",
+          !opt_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_rtc_read();
+
+    case WALLCLOCK_EFI:
+        return efi_get_time();
+
+    case WALLCLOCK_UNSET:
+        /* Unexpected state - handled by the ASSERT_UNREACHABLE() below. */
+        break;
+    }
+
+    ASSERT_UNREACHABLE();
+    return 0;
 }
 
 /***************************************************************************
@@ -2463,6 +2525,10 @@ 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());
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging