[xen staging] x86/HPET: don't enable legacy replacement mode unconditionally

[patchbot@xxxxxxx]

commit e680cc48b7184d3489873d6776f84ba1fc238ced
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Mar 24 11:34:32 2021 +0100
Commit:     Ian Jackson <iwj@xxxxxxxxxxxxxx>
CommitDate: Fri Mar 26 17:02:55 2021 +0000

    x86/HPET: don't enable legacy replacement mode unconditionally
    
    Commit e1de4c196a2e ("x86/timer: Fix boot on Intel systems using ITSSPRC
    static PIT clock gating") was reported to cause boot failures on certain
    AMD Ryzen systems. Until we can figure out what the actual issue there
    is, skip this new part of HPET setup by default. Introduce a "hpet"
    command line option to allow enabling this on hardware where it's really
    needed for Xen to boot successfully (i.e. where the PIT doesn't drive
    the timer interrupt).
    
    Since it makes little sense to introduce just "hpet=legacy-replacement",
    also allow for a boolean argument as well as "broadcast" to replace the
    separate "hpetbroadcast" option.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
 docs/misc/xen-command-line.pandoc | 17 +++++++++++++++++
 xen/arch/x86/hpet.c               | 37 +++++++++++++++++++++++++++++++------
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index a0601ff838..deef6d0b4c 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1274,9 +1274,26 @@ 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>`
 
diff --git a/xen/arch/x86/hpet.c b/xen/arch/x86/hpet.c
index 1ff005fb4a..76d9ef2c02 100644
--- a/xen/arch/x86/hpet.c
+++ b/xen/arch/x86/hpet.c
@@ -52,6 +52,8 @@ 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;
 
@@ -63,6 +65,32 @@ 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:
@@ -761,12 +789,9 @@ u64 __init hpet_setup(void)
     unsigned int hpet_id, hpet_period, hpet_cfg;
     unsigned int last, rem;
 
-    if ( hpet_rate )
+    if ( hpet_rate || !hpet_address || !opt_hpet )
         return hpet_rate;
 
-    if ( hpet_address == 0 )
-        return 0;
-
     set_fixmap_nocache(FIX_HPET_BASE, hpet_address);
 
     hpet_id = hpet_read32(HPET_ID);
@@ -803,9 +828,9 @@ u64 __init hpet_setup(void)
      * IRQ routing is configured.
      *
      * Reconfigure the HPET into legacy mode to re-establish the timer
-     * interrupt.
+     * interrupt, if available and if so requested.
      */
-    if ( hpet_id & HPET_ID_LEGSUP &&
+    if ( opt_legacy_replacement && (hpet_id & HPET_ID_LEGSUP) &&
          !((hpet_cfg = hpet_read32(HPET_CFG)) & HPET_CFG_LEGACY) )
     {
         unsigned int c0_cfg, ticks, count;
--
generated by git-patchbot for /home/xen/git/xen.git#staging