diff mbox

virt-acpi-build: add always-on property for timer

Message ID 1453380893-26174-1-git-send-email-drjones@redhat.com
State Superseded
Headers show

Commit Message

Andrew Jones Jan. 21, 2016, 12:54 p.m. UTC
This patch is the ACPI equivalent of "hw/arm/virt: Add always-on
property to the virt board timer". The timer is always on, and
thus setting this informs Linux that it may switch off the periodic
timer. Switching off the periodic timer substantially reduces the
number of interrupts the host needs to inject.

Testing note: AArch64 guests (the only ones currently booting with
ACPI) do not actually need this patch to determine it can turn the
periodic timer off. I therefore used a hacked guest kernel to ensure
this patch works as the equivalent DT patch does.

Signed-off-by: Andrew Jones <drjones@redhat.com>

---
 hw/arm/virt-acpi-build.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
1.8.3.1

Comments

Peter Maydell Jan. 25, 2016, 11:56 a.m. UTC | #1
On 21 January 2016 at 12:54, Andrew Jones <drjones@redhat.com> wrote:
> This patch is the ACPI equivalent of "hw/arm/virt: Add always-on

> property to the virt board timer". The timer is always on, and

> thus setting this informs Linux that it may switch off the periodic

> timer. Switching off the periodic timer substantially reduces the

> number of interrupts the host needs to inject.

>

> Testing note: AArch64 guests (the only ones currently booting with

> ACPI) do not actually need this patch to determine it can turn the

> periodic timer off. I therefore used a hacked guest kernel to ensure

> this patch works as the equivalent DT patch does.

>

> Signed-off-by: Andrew Jones <drjones@redhat.com>




Applied to target-arm.next, thanks.

-- PMM
diff mbox

Patch

diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 87fbe7c97d99b..f6e538f3d02ea 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -443,7 +443,7 @@  build_gtdt(GArray *table_data, GArray *linker)
     gtdt->secure_el1_flags = ACPI_EDGE_SENSITIVE;
 
     gtdt->non_secure_el1_interrupt = ARCH_TIMER_NS_EL1_IRQ + 16;
-    gtdt->non_secure_el1_flags = ACPI_EDGE_SENSITIVE;
+    gtdt->non_secure_el1_flags = ACPI_EDGE_SENSITIVE | ACPI_GTDT_ALWAYS_ON;
 
     gtdt->virtual_timer_interrupt = ARCH_TIMER_VIRT_IRQ + 16;
     gtdt->virtual_timer_flags = ACPI_EDGE_SENSITIVE;