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From: Mark Rutland <mark.rutland@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 1/3] arm64: perf: Add support caps in sysfs
Date: Mon, 20 Jul 2020 11:50:19 +0100	[thread overview]
Message-ID: <20200720105019.GA54220@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20200720101518.GA11516@willie-the-truck>

On Mon, Jul 20, 2020 at 11:15:19AM +0100, Will Deacon wrote:
> On Thu, Jun 18, 2020 at 09:35:42PM +0800, Shaokun Zhang wrote:

> > +static umode_t
> > +armv8pmu_caps_attr_is_visible(struct kobject *kobj, struct attribute *attr,
> > +			      int unused)
> > +{
> > +	int pmuver = armv8pmu_get_pmu_version();
> > +
> > +	if (pmuver >= ID_AA64DFR0_PMUVER_8_4)
> > +		return attr->mode;
> 
> Is this sufficient? I'm a bit confused by the text in the Arm ARM that says:
> 
>   | If ARMv8.4-PMU is implemented:
>   | * If STALL_SLOT is not implemented, it is IMPLEMENTATION DEFINED whether
>   |   the PMMIR System registers are implemented.
>   | * If STALL_SLOT is implemented, then the PMMIR System registers are
>   |   implemented.
> 
> whereas the register description for PMMIR_EL1 says:
> 
>   | This register is present only when ARMv8.4-PMU is implemented.

I think this is trying to say that when ARMv8.4-PMU is not implemented,
PMMIR definitely isn't implemented (i.e. the the presence of PMMIR_EL1
implies the presence of ARMv8.4-PMU).

> Mark -- please could you clarify whether or not we need to check STALL_SLOT
> as well as the PMUVer?

Given the explciit wording that it's IMP DEF, I suspect that we need to
check both.

I'll go chase this up.

Mark.

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  reply	other threads:[~2020-07-20 10:51 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-18 13:35 [PATCH v3 1/3] arm64: perf: Add support caps in sysfs Shaokun Zhang
2020-06-18 13:35 ` [PATCH v3 2/3] arm64: perf: Expose some new events via sysfs Shaokun Zhang
2020-07-20 10:16   ` Will Deacon
2020-06-18 13:35 ` [PATCH v3 3/3] arm64: perf: Correct the event index in sysfs Shaokun Zhang
2020-07-20 10:20   ` Will Deacon
2020-07-07 13:33 ` [PATCH v3 1/3] arm64: perf: Add support caps " Shaokun Zhang
2020-07-20 10:15 ` Will Deacon
2020-07-20 10:50   ` Mark Rutland [this message]
2020-07-20 10:54     ` Will Deacon
2020-07-20 13:11       ` Shaokun Zhang
2020-07-21  8:05       ` Shaokun Zhang

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