[RFT] arm64: dts: qcom: sc7280: Add missing LMH interrupts

Hook up the interrupts that signal the Limits Management Hardware has
started some sort of throttling action.

Fixes: 7dbd121a2c58 ("arm64: dts: qcom: sc7280: Add cpufreq hw node")
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
---
test case:

- hammer the CPUs (like compile the Linux kernel)
- watch -n1 "cat /proc/interrupts | grep dcvsh"
- the numbers go up up up up -> good
---
 arch/arm64/boot/dts/qcom/sc7280.dtsi | 8 ++++++++
 1 file changed, 8 insertions(+)


---
base-commit: 21ef7b1e17d039053edaeaf41142423810572741
change-id: 20230811-topic-7280_lmhirq-e07ad2530387

Best regards,

Hi,

On Fri, Aug 11, 2023 at 1:58 PM Konrad Dybcio <konrad.dybcio@linaro.org> wrote:
>
> Hook up the interrupts that signal the Limits Management Hardware has
> started some sort of throttling action.
>
> Fixes: 7dbd121a2c58 ("arm64: dts: qcom: sc7280: Add cpufreq hw node")
> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
> ---
> test case:
>
> - hammer the CPUs (like compile the Linux kernel)
> - watch -n1 "cat /proc/interrupts | grep dcvsh"
> - the numbers go up up up up -> good

I'm not doing much on sc7280 these days, but I did try putting your
patch on a sc7280-hoglin (AKA a CRD). I tried to stress the system out
a bunch (ran 8 instances of "while true; do true; done" and opened
something to activate the GPU). I didn't see any LMH interrupts fire.
Of course, with ChromeOS firmware LMH is _supposed_ to be mostly
disabled, so maybe that's right? Our policy was always to have Linux
do as much of the throttling as possible and only use LMH as a last
resort.

I assume I don't need any specific config option turned on?

I know that on other Qualcomm boards I see LMH nodes in the device
tree, which we don't have in sc7280. Like "qcom,sdm845-lmh". Is that
important? I haven't been following what's been going on with LMH in
Linux since we try not to use it.

For giggles, I also tried putting the patch on a sc7280-villager
device to see if it had different thermals. I even put my jacket over
it to try to keep it warm. I saw the sensors go up to 109C on the
medium cores and still no LMH interrupts. Oh, and then the device shut
itself down. I guess something about thermal throttling in Linux must
be disabled but then it still handles the critical state? :( That's
concerning...

I put the same kernel on a trogdor device and that did normal Linux
throttling OK. So something is definitely wonky with sc7280... I dug
enough to find that if I used "step_wise" instead of "power_allocator"
that it works OK, so I guess something is wonky about the config of
power_allocator on sc7280. In any case, it's not affected by your
patch and I've already probably spent too much time on it. :-P

-Doug

On 25.08.2023 22:17, Doug Anderson wrote:
> Hi,
> 
> On Fri, Aug 11, 2023 at 1:58 PM Konrad Dybcio <konrad.dybcio@linaro.org> wrote:
>>
>> Hook up the interrupts that signal the Limits Management Hardware has
>> started some sort of throttling action.
>>
>> Fixes: 7dbd121a2c58 ("arm64: dts: qcom: sc7280: Add cpufreq hw node")
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
>> ---
>> test case:
>>
>> - hammer the CPUs (like compile the Linux kernel)
>> - watch -n1 "cat /proc/interrupts | grep dcvsh"
>> - the numbers go up up up up -> good
> 
> I'm not doing much on sc7280 these days,
:( I'm really sad it got the boot

but I did try putting your
> patch on a sc7280-hoglin (AKA a CRD). I tried to stress the system out
> a bunch (ran 8 instances of "while true; do true; done" and opened
> something to activate the GPU). I didn't see any LMH interrupts fire.
> Of course, with ChromeOS firmware LMH is _supposed_ to be mostly
> disabled, so maybe that's right? Our policy was always to have Linux
> do as much of the throttling as possible and only use LMH as a last
> resort.
> 
> I assume I don't need any specific config option turned on?
> 
> I know that on other Qualcomm boards I see LMH nodes in the device
> tree, which we don't have in sc7280. Like "qcom,sdm845-lmh". Is that
> important? I haven't been following what's been going on with LMH in
> Linux since we try not to use it.
It used to be important, but on newer socs it's preconfigured in fw

> 
> For giggles, I also tried putting the patch on a sc7280-villager
> device to see if it had different thermals. I even put my jacket over
> it to try to keep it warm. I saw the sensors go up to 109C on the
> medium cores and still no LMH interrupts. Oh, and then the device shut
> itself down. I guess something about thermal throttling in Linux must
> be disabled but then it still handles the critical state? :( That's
> concerning...
> 
> I put the same kernel on a trogdor device and that did normal Linux
> throttling OK. So something is definitely wonky with sc7280... I dug
> enough to find that if I used "step_wise" instead of "power_allocator"
> that it works OK, so I guess something is wonky about the config of
> power_allocator on sc7280. In any case, it's not affected by your
> patch and I've already probably spent too much time on it. :-P
Hm, perhaps it would be worth to try this patch on a non-chrome 7280
device.. Would you guys have standard android-y or windows-y firmware
that you could flash on these to try out, or should I try poking
somebody else?

Konrad

Hi,

On Fri, Aug 25, 2023 at 2:07 PM Konrad Dybcio <konrad.dybcio@linaro.org> wrote:
>
> > I put the same kernel on a trogdor device and that did normal Linux
> > throttling OK. So something is definitely wonky with sc7280... I dug
> > enough to find that if I used "step_wise" instead of "power_allocator"
> > that it works OK, so I guess something is wonky about the config of
> > power_allocator on sc7280. In any case, it's not affected by your
> > patch and I've already probably spent too much time on it. :-P
> Hm, perhaps it would be worth to try this patch on a non-chrome 7280
> device.. Would you guys have standard android-y or windows-y firmware
> that you could flash on these to try out, or should I try poking
> somebody else?

I don't have hardware that runs anything other than the standard
ChromeOS bootloader, sorry!

-Doug