Re: [PATCH v3 2/2] arm64: dts: Fix broken architected timer interrupt trigger

[Marc Zyngier]

On Thu, 09 Jun 2016 14:06:02 -0700
David Daney <ddaney.cavm@xxxxxxxxx> wrote:

> I spoke too soon...
> 
> On 06/09/2016 11:11 AM, David Daney wrote:
> > On 06/06/2016 10:56 AM, Marc Zyngier wrote:
> >> The ARM architected timer specification mandates that the interrupt
> >> associated with each timer is level triggered (which corresponds to
> >> the "counter >= comparator" condition).
> >>
> >> A number of DTs are being remarkably creative, declaring the interrupt
> >> to be edge triggered. A quick look at the TRM for the corresponding ARM
> >> CPUs clearly shows that this is wrong, and I've corrected those.
> >> For non-ARM designs (and in the absence of a publicly available TRM),
> >> I've made them active low as well, which can't be completely wrong
> >> as the GIC cannot disinguish between level low and level high.
> >>
> >> The respective maintainers are of course welcome to prove me wrong.
> >>
> >> While I was at it, I took the liberty to fix a couple of related issue,
> >> such as some spurious affinity bits on ThunderX, and their complete
> >> absence on ls1043a (both of which seem to be related to copy-pasting
> >> from other DTs).
> >>
> >> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> >> ---
> >>   arch/arm64/boot/dts/altera/socfpga_stratix10.dtsi    | 8 ++++----
> >>   arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi          | 8 ++++----
> >>   arch/arm64/boot/dts/apm/apm-storm.dtsi               | 8 ++++----
> >>   arch/arm64/boot/dts/broadcom/ns2.dtsi                | 8 ++++----
> >>   arch/arm64/boot/dts/cavium/thunder-88xx.dtsi         | 8 ++++----
> >>   arch/arm64/boot/dts/exynos/exynos7.dtsi              | 8 ++++----
> >>   arch/arm64/boot/dts/freescale/fsl-ls1043a.dtsi       | 8 ++++----
> >>   arch/arm64/boot/dts/marvell/armada-ap806.dtsi        | 8 ++++----
> >>   arch/arm64/boot/dts/socionext/uniphier-ph1-ld20.dtsi | 8 ++++----
> >>   arch/arm64/boot/dts/xilinx/zynqmp.dtsi               | 8 ++++----
> >>   10 files changed, 40 insertions(+), 40 deletions(-)
> >>
> > [...]
> >> diff --git a/arch/arm64/boot/dts/cavium/thunder-88xx.dtsi
> >> b/arch/arm64/boot/dts/cavium/thunder-88xx.dtsi
> >> index 2eb9b22..382d86f 100644
> >> --- a/arch/arm64/boot/dts/cavium/thunder-88xx.dtsi
> >> +++ b/arch/arm64/boot/dts/cavium/thunder-88xx.dtsi
> >> @@ -354,10 +354,10 @@
> >>
> >>       timer {
> >>           compatible = "arm,armv8-timer";
> >> -        interrupts = <1 13 0xff01>,
> >> -                     <1 14 0xff01>,
> >> -                     <1 11 0xff01>,
> >> -                     <1 10 0xff01>;
> >> +        interrupts = <1 13 8>,
> >> +                     <1 14 8>,
> >> +                     <1 11 8>,
> >> +                     <1 10 8>;
> 
> 
> NAK!
> 
> According to arm,gic-v3.txt the trigger value must be either 1 or 4:
> 
>    The 3rd cell is the flags, encoded as follows:
>          bits[3:0] trigger type and level flags.
>                  1 = edge triggered
>                  4 = level triggered

Which is a bug in the binding description. PPIs can be any trigger
(just look at the TRM for CPUs that have devices connected to a PPI to
be convinced - most of them are level low).

This doesn't mean that you can distinguish level-high from level-low
in a programmatic way. But the HW definitely can handle it.

I'll update the GICv3 binding to reflect this.

Now, coming back to your NAK: is level-low the right or wrong trigger
for your implementation of the architected timers?

Thanks,

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