Re: [PATCH] arm64: dts: allwinner: a64: Drop PMU node
From: Maxime Ripard <hidden>
Date: 2019-08-08 16:26:28
Also in:
linux-devicetree
On Wed, Aug 07, 2019 at 10:36:08AM -0700, Vasily Khoruzhick wrote:
On Wed, Aug 7, 2019 at 4:56 AM Maxime Ripard [off-list ref] wrote:quoted
On Tue, Aug 06, 2019 at 07:39:26PM -0700, Vasily Khoruzhick wrote:quoted
On Tue, Aug 6, 2019 at 2:14 PM Robin Murphy [off-list ref] wrote:quoted
On 2019-08-06 9:52 pm, Vasily Khoruzhick wrote:quoted
On Tue, Aug 6, 2019 at 1:19 PM Harald Geyer [off-list ref] wrote:quoted
Vasily Khoruzhick writes:quoted
On Tue, Aug 6, 2019 at 7:35 AM Robin Murphy [off-list ref] wrote:quoted
On 06/08/2019 15:01, Vasily Khoruzhick wrote:quoted
Looks like PMU in A64 is broken, it generates no interrupts at all and as result 'perf top' shows no events.Does something like 'perf stat sleep 1' at least count cycles correctly? It could well just be that the interrupt numbers are wrong...Looks like it does, at least result looks plausible:I'm using perf stat regularly (cache benchmarks) and it works fine. Unfortunately I wasn't aware that perf stat is a poor test for the interrupts part of the node, when I added it. So I'm not too surprised I got it wrong. However, it would be unfortunate if the node got removed completely, because perf stat would not work anymore. Maybe we can only remove the interrupts or just fix them even if the HW doesn't work?I'm not familiar with PMU driver. Is it possible to get it working without interrupts?Yup - you get a grumpy message from the driver, it will refuse sampling events (the ones which weren't working anyway), and if you measure anything for long enough that a counter overflows you'll get wonky results. But for counting hardware events over relatively short periods it'll still do the job.I tried to drop interrupts completely from the node but 'perf top' is still broken. Though now in different way: it complains "cycles: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'"I have no idea if that's the culprit, but what is the state of the 0x09010000 register?What register is that and how do I check it?
It's in the CPUX Configuration block, and the bits are labelled as CPU Debug Reset. And if you have busybox, you can use devmem. Maxime -- Maxime Ripard, Bootlin Embedded Linux and Kernel engineering https://bootlin.com