[PATCH v4 1/9] clocksource: arm_arch_timer: Gather KVM specific information in a structure

Daniel,

On 29/03/16 18:13, Daniel Lezcano wrote:

On 03/24/2016 06:53 PM, Julien Grall wrote:

quoted

Introduce a structure which are filled up by the arch timer driver and
used by the virtual timer in KVM.

The first member of this structure will be the timecounter. More members
will be added later.

A stub for the new helper isn't introduced because KVM requires the arch
timer for both ARM64 and ARM32.

The function arch_timer_get_timecounter is kept for the time being and
will be dropped in a subsequent patch.

Signed-off-by: Julien Grall <redacted>

quoted

Cc: Daniel Lezcano <redacted>
Cc: Thomas Gleixner <redacted>
Cc: Marc Zyngier <redacted>

     Changes in v3:
         - Rename the patch
         - Move the KVM changes and removal of arch_timer_get_timecounter
         in separate patches.
---
  drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
  include/clocksource/arm_arch_timer.h |  5 +++++
  2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 5152b38..62bdfe7 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c

@@ -468,11 +468,16 @@ static struct cyclecounter cyclecounter = {
  	.mask	= CLOCKSOURCE_MASK(56),
  };

-static struct timecounter timecounter;
+static struct arch_timer_kvm_info arch_timer_kvm_info;

This structure is statically defined in this subsystem but not used in 
this file and a couple of a accessors is added to let another subsystem 
to access it.

That sounds there is something wrong here with the design of the current 
code, virt/phys are mixed.

It isn't possible to split the virt/phys timer code respectively in 
virt/kvm/arm/arch_timer.c and drivers/clocksource/arm_arch_timer.c ?

No, that'd be the wrong thing to do. The kernel uses *either* the virt
or phys timer depending on how it has been booted, and both counters are
in use.

What KVM (or any other hypervisor) needs from the timer subsystem is:
- an interrupt (so that it can force a guest exit when the timer fires),
- a way to convert the values programmed into the HW into a timer event
(which is what the time counter structure is for).

That allows the hypervisor to *emulate* a timer for the guest, and
that's what virt/kvm/arm/arch_timer.c is all about. We have a clear
separation of what is driving the HW vs what is emulating it, and I'm
quite eager to preserve that.

At least, 'struct arch_timer_kvm_info' should belong to 
virt/kvm/arm/arch_timer.c.

At the cost of mandating separate storage in the arm_arch_timer driver.
I do not find that much nicer, but if you prefer that, fine by me.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...