diff mbox series

[XEN,v3] x86/hpet: Disable legacy replacement mode after IRQ test

Message ID 20230807113117.1277-1-simon@invisiblethingslab.com (mailing list archive)
State New, archived
Headers show
Series [XEN,v3] x86/hpet: Disable legacy replacement mode after IRQ test | expand

Commit Message

Simon Gaiser Aug. 7, 2023, 11:31 a.m. UTC 
As far as I understand the HPET legacy mode is not required after the
timer IRQ test. For previous discussion see [1] and [2]. Keeping it
enabled prevents reaching deeper C-states on some systems and thereby
also S0ix residency. So disable it after the timer IRQ test worked. Note
that this code path is only reached when opt_hpet_legacy_replacement < 0,
so explicit user choice is still honored.

Link: https://lore.kernel.org/xen-devel/cb408368-077d-edb5-b4ad-f80086db48c1@invisiblethingslab.com/ # [1]
Link: https://lore.kernel.org/xen-devel/20230718122603.2002-1-simon@invisiblethingslab.com/ # [2]
Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>
---

[ Resending v3, now with a unique Message-ID, sorry. ]

Changes in v3:

 - Edit log message and downgrade it to XENLOG_DEBUG.

Changes in v2:

 - Always disable legacy mode after test, not only when ARAT is
   available. See [3] for reasoning.

[3]: https://lore.kernel.org/xen-devel/ac77ecba-6804-1d16-60dc-f184e5d31dcb@invisiblethingslab.com/

---
 xen/arch/x86/io_apic.c | 2 ++
 1 file changed, 2 insertions(+)
diff mbox series

Patch

diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index 041233b9b7..b4b4cd5939 100644
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -1967,6 +1967,8 @@  static void __init check_timer(void)
 
             if ( timer_irq_works() )
             {
+                printk(XENLOG_DEBUG "IRQ test with HPET Legacy Replacement Mode worked - disabling it again\n");
+                hpet_disable_legacy_replacement_mode();
                 local_irq_restore(flags);
                 return;
             }