Re: [PATCH] arm: bcm2835: Add the PMU to the devicetree.

From: Florian Fainelli <f.fainelli@gmail.com>
To: Vince Weaver <vincent.weaver@maine.edu>,
	Peter Zijlstra <peterz@infradead.org>,
	marc.zyngier@arm.com
Cc: Stefan Wahren <stefan.wahren@i2se.com>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	linux-rpi-kernel@lists.infradead.org,
	bcm-kernel-feedback-list@broadcom.com,
	linux-kernel@vger.kernel.org, Eric Anholt <eric@anholt.net>,
	linux-arm-kernel@lists.infradead.org,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH] arm: bcm2835: Add the PMU to the devicetree.
Date: Thu, 17 May 2018 12:59:28 -0700	[thread overview]
Message-ID: <0a643984-1586-8c56-6627-430f0c2a4ba8@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1805171530080.8529@macbook-air>

On 05/17/2018 12:31 PM, Vince Weaver wrote:
> On Thu, 17 May 2018, Vince Weaver wrote:
> 
>> On Thu, 17 May 2018, Peter Zijlstra wrote:
>> with cortex-a7 now, would it be possible to later drop that if proper 
>> cortex-a53 support is added to the armv7 pmu driver?  Or would that lead 
>> to all kinds of back-compatability mess?
> 
> For what it's worth, the pi-foundation kernel bcm2710 device tree file 
> does:
> 
> 		arm-pmu {
> #ifdef RPI364
> 			compatible = "arm,armv8-pmuv3", "arm,cortex-a7-pmu";
> #else
> 			compatible = "arm,cortex-a7-pmu";
> #endif
> 			interrupt-parent = <&local_intc>;
> 			interrupts = <9>;
> 		};
> 
> 
> Which is probably where I was getting the arm,armv8-pmuv3 from in my 
> original patch.

I thought somehow that Marc Z. had unified
arch/arm/kernel/perf_event_v7.c and arch/arm64/kernel/perf_event.c into
a common driver entry point under drivers/perf/arm_pmu.c but I don't see
it and after about 15 minutes looking at it, it does not look as trivial
as I though to separate out those files so the ARMv8 PMU description can
be moved into a generic location for instance.

FWIW, Broadcom STB chips, even when 64-bit capable or often used with an
32-bit ARM kernel, so having the ARMv8 PMUs work under a 32-bit ARM
kernel would be great. The downstream solution we have sued thus far is
to find the closest compatible string to represent those, which is not
great...
-- 
Florian