Revert "x86/HPET: don't enable legacy replacement mode unconditionally"

This reverts commit e680cc48b7.

It was committed despite multiple objections.  The agreed upon fix is a
different variation of the same original patch, and the delta between the two
is far from clear.

By reverting this commit first, the fixes are clear and coherent as individual
patches, and in the appropriate form for backport to the older trees.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 2b05d427a0
master date: 2021-04-15 18:25:40 +0100

docs/misc/xen-command-line.pandoc

@@ -1274,26 +1274,9 @@ supported. See docs/misc/arm/big.LITTLE.txt for more information.
 When the hmp-unsafe option is disabled (default), CPUs that are not
 identical to the boot CPU will be parked and not used by Xen.
 
-### hpet (x86)
-> `= List of [ <boolean> | broadcast | legacy-replacement ]`
-
-> Default : `true`, `no-broadcast`, 'no-legacy-replacement`
-
-Controls Xen's use of the system's High Precision Event Timer.  The boolean
-allows to turn off use altogether.
-
-`broadcast` forces Xen to keep using the broadcast for CPUs in deep C-states
-even when an RTC interrupt got enabled.
-
-`legacy-replacement` is intended to be used on platforms where the timer
-interrupt doesn't get raised by the legacy PIT.  This then also affects
-raising of the RTC interrupt.
-
 ### hpetbroadcast (x86)
 > `= <boolean>`
 
-Deprecated alternative of `hpet=broadcast`.
-
 ### hvm_debug (x86)
 > `= <integer>`
 

xen/arch/x86/hpet.c

@@ -52,8 +52,6 @@ static unsigned int __read_mostly num_hpets_used;
 DEFINE_PER_CPU(struct hpet_event_channel *, cpu_bc_channel);
 
 unsigned long __initdata hpet_address;
-static bool __initdata opt_hpet = true;
-static bool __initdata opt_legacy_replacement;
 u8 __initdata hpet_blockid;
 u8 __initdata hpet_flags;
 
@@ -65,32 +63,6 @@ u8 __initdata hpet_flags;
 static bool __initdata force_hpet_broadcast;
 boolean_param("hpetbroadcast", force_hpet_broadcast);
 
-static int __init parse_hpet_param(const char *s)
-{
-    const char *ss;
-    int val, rc = 0;
-
-    do {
-        ss = strchr(s, ',');
-        if ( !ss )
-            ss = strchr(s, '\0');
-
-        if ( (val = parse_bool(s, ss)) >= 0 )
-            opt_hpet = val;
-        else if ( (val = parse_boolean("broadcast", s, ss)) >= 0 )
-            force_hpet_broadcast = val;
-        else if ( (val = parse_boolean("legacy-replacement", s, ss)) >= 0 )
-            opt_legacy_replacement = val;
-        else
-            rc = -EINVAL;
-
-        s = ss + 1;
-    } while ( *ss );
-
-    return rc;
-}
-custom_param("hpet", parse_hpet_param);
-
 /*
  * Calculate a multiplication factor for scaled math, which is used to convert
  * nanoseconds based values to clock ticks:
@@ -789,9 +761,12 @@ u64 __init hpet_setup(void)
     unsigned int hpet_id, hpet_period, hpet_cfg;
     unsigned int last, rem;
 
-    if ( hpet_rate || !hpet_address || !opt_hpet )
+    if ( hpet_rate )
         return hpet_rate;
 
+    if ( hpet_address == 0 )
+        return 0;
+
     set_fixmap_nocache(FIX_HPET_BASE, hpet_address);
 
     hpet_id = hpet_read32(HPET_ID);
@@ -828,9 +803,9 @@ u64 __init hpet_setup(void)
      * IRQ routing is configured.
      *
      * Reconfigure the HPET into legacy mode to re-establish the timer
-     * interrupt, if available and if so requested.
+     * interrupt.
      */
-    if ( opt_legacy_replacement && (hpet_id & HPET_ID_LEGSUP) &&
+    if ( hpet_id & HPET_ID_LEGSUP &&
          !((hpet_cfg = hpet_read32(HPET_CFG)) & HPET_CFG_LEGACY) )
     {
         unsigned int c0_cfg, ticks, count;