linux-kernel - Re: [Qemu-devel] arm64 qemu tests failing in linux-next since 'arm64: kernel: enforce pmuserenr

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Message-ID: <CAFEAcA_vP93=PE6LNNHodCsdk0gL0kBQPX=xzLJU5RzkvNs2vw@mail.gmail.com>
Date:	Thu, 7 Jan 2016 15:58:15 +0000
From:	Peter Maydell <peter.maydell@...aro.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	Will Deacon <will.deacon@....com>,
	QEMU Developers <qemu-devel@...gnu.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Qemu-devel] arm64 qemu tests failing in linux-next since 'arm64:
 kernel: enforce pmuserenr_el0 initialization and restore'

On 7 January 2016 at 15:53, Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:
> On Thu, Jan 07, 2016 at 01:25:35PM +0000, Peter Maydell wrote:
>> We had previously been relying on the kernel not attempting to
>> touch the PMU if the ID_AA64DFR0_EL1 PMUVer bits read 0000
>> ("Performance Monitors extension System registers not implemented").
>
> Ok, thanks for looking into this. I wonder why reading pmcr_el0 does
> not suffer from the same problem though.

Just a pragmatic thing on QEMU's end, I expect -- the kernel already
touched PMCR_EL0 and we wanted to be able to boot it, so we have an
implementation of it.

thanks
-- PMM
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