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

[Marc Zyngier]

On 10/06/16 17:50, David Daney wrote:
> On 06/10/2016 12:23 AM, Marc Zyngier wrote:
>> 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?
>>
> 
> For the Cavium Thunder implementation of GIC-v3, there is no concept of 
> high and low.  All we have is asserted and not-asserted, we have chosen 
> to map the concept of an asserted level-triggered source to 
> IRQ_TYPE_LEVEL_HIGH, and the transition from not-asserted to asserted on 
> an edge triggered source to IRQ_TYPE_EDGE_RISING.

The GIC, no matter if it is from Cavium or not, doesn't have a notion of
high or low indeed *from a programming interface point of view*. What
matters here is the *device*, and how it is connected to the interrupt
controller. And I'm pretty sure your timers are *physically* one or the
other (unless they are simply floating? ;-)

Thanks,

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