[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [RFC PATCH 17/49] ARM: timer: Handle level triggered IRQs correctly

On 12/02/18 18:23, Andre Przywara wrote:

Hi Andre,

On 12/02/18 15:19, Julien Grall wrote:
Hi Andre,

On 09/02/18 14:39, Andre Przywara wrote:
The ARM Generic Timer uses a level-sensitive interrupt semantic. We
easily catch when the line goes high, as this triggers the hardware IRQ.
However we have to sync the state of the interrupt condition at certain
points to catch when the line goes low and we can remove the vtimer vIRQ
from the vGIC (and the LR).
The VGIC in Xen so far only implemented edge triggered vIRQs, really, so
we need to add new functionality to re-sample the interrupt state.

You might want to make a summary of the discussion we had with Marc Z.
today here. This would help the other to understand why sample the
interrupt state is necessary :).

Yes, I just saw that I somehow missed copying the elaborate comment from
Christoffer. Fixed now, indeed without this background it's next to
impossible to understand this ;-)

Also do we need to do that for the emulated physical timer?

Mmh, good question. I believe this whole timer story needs a good think

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxx>
   xen/arch/arm/time.c     | 34 ++++++++++++++++++++++++++++++++++
   xen/arch/arm/traps.c    |  1 +
   xen/include/xen/timer.h |  2 ++
   3 files changed, 37 insertions(+)

diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c
index c11fcfeadd..98ebb4305d 100644
--- a/xen/arch/arm/time.c
+++ b/xen/arch/arm/time.c
@@ -263,6 +263,40 @@ static void vtimer_interrupt(int irq, void
*dev_id, struct cpu_user_regs *regs)
       vgic_inject_irq(current->domain, current,
current->arch.virt_timer.irq, true);

One * is enough.

That's kernel-doc comment style:

That allows tools to scan the tree and extract function documentation in
an automated way. A bit like markdown: still perfectly readable by
humans, but parse-able by scripts as well.

I was hoping that it wouldn't hurt to have this in Xen as well, as I
copied this already in other parts of this code.

I was blindly following the CODING_STYLE requirements :). But let's keep /** if it helps script.


Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.