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From: Richard Cochran <richardcochran@gmail.com>
To: Jianyong Wu <jianyong.wu@arm.com>
Cc: Mark.Rutland@arm.com, maz@kernel.org, justin.he@arm.com,
	Wei.Chen@arm.com, kvm@vger.kernel.org, suzuki.poulose@arm.com,
	netdev@vger.kernel.org, Steve.Capper@arm.com,
	linux-kernel@vger.kernel.org, sean.j.christopherson@intel.com,
	steven.price@arm.com, Kaly.Xin@arm.com, john.stultz@linaro.org,
	yangbo.lu@nxp.com, pbonzini@redhat.com, tglx@linutronix.de,
	nd@arm.com, will@kernel.org, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH v12 10/11] arm64: add mechanism to let user choose which counter to return
Date: Sat, 23 May 2020 19:11:06 -0700
Message-ID: <20200524021106.GC335@localhost> (raw)
In-Reply-To: <20200522083724.38182-11-jianyong.wu@arm.com>

On Fri, May 22, 2020 at 04:37:23PM +0800, Jianyong Wu wrote:
> In general, vm inside will use virtual counter compered with host use
> phyical counter. But in some special scenarios, like nested
> virtualization, phyical counter maybe used by vm. A interface added in
> ptp_kvm driver to offer a mechanism to let user choose which counter
> should be return from host.

Sounds like you have two time sources, one for normal guest, and one
for nested.  Why not simply offer the correct one to user space
automatically?  If that cannot be done, then just offer two PHC
devices with descriptive names.

> diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
> index fef72f29f3c8..8b0a7b328bcd 100644
> --- a/drivers/ptp/ptp_chardev.c
> +++ b/drivers/ptp/ptp_chardev.c
> @@ -123,6 +123,9 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
>  	struct timespec64 ts;
>  	int enable, err = 0;
>  
> +#ifdef CONFIG_ARM64
> +	static long flag;

static?  This is not going to fly.

> +		 * In most cases, we just need virtual counter from host and
> +		 * there is limited scenario using this to get physical counter
> +		 * in guest.
> +		 * Be careful to use this as there is no way to set it back
> +		 * unless you reinstall the module.

How on earth is the user supposed to know this?

From your description, this "flag" really should be a module
parameter.

Thanks,
Richard

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  parent reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-22  8:37 [RFC PATCH v12 0/11] Enable ptp_kvm for arm64 Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 01/11] arm64: Probe for the presence of KVM hypervisor services during boot Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 02/11] arm/arm64: KVM: Advertise KVM UID to guests via SMCCC Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 03/11] psci: export smccc conduit get helper Jianyong Wu
2020-05-22 13:12   ` Sudeep Holla
2020-05-25  1:37     ` Jianyong Wu
2020-05-26 10:10       ` Sudeep Holla
2020-05-27  1:18         ` Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 04/11] ptp: Reorganize ptp_kvm modules to make it arch-independent Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 05/11] time: Add mechanism to recognize clocksource in time_get_snapshot Jianyong Wu
2020-05-28 16:36   ` Thomas Gleixner
2020-05-29  1:05     ` Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 06/11] clocksource: Add clocksource id for arm arch counter Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 07/11] psci: Add hypercall service for kvm ptp Jianyong Wu
2020-05-22 14:18   ` Steven Price
2020-05-25  2:11     ` Jianyong Wu
2020-05-26 11:02       ` Steven Price
2020-05-27  6:06         ` Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 08/11] ptp: arm64: Enable ptp_kvm for arm/arm64 Jianyong Wu
2020-05-22  8:37 ` [RFC PATCH v12 09/11] ptp: extend input argument for getcrosstimestamp API Jianyong Wu
2020-05-24  1:42   ` Richard Cochran
2020-05-22  8:37 ` [RFC PATCH v12 10/11] arm64: add mechanism to let user choose which counter to return Jianyong Wu
2020-05-24  1:47   ` Richard Cochran
2020-05-24  2:11   ` Richard Cochran [this message]
2020-05-25  4:50     ` Jianyong Wu
2020-05-25  6:16       ` Richard Cochran
2020-05-25  6:29         ` Jianyong Wu
2020-05-25  9:17     ` Marc Zyngier
2020-05-25 14:18       ` Jianyong Wu
2020-05-25 15:28         ` Marc Zyngier
2020-05-22  8:37 ` [RFC PATCH v12 11/11] arm64: Add kvm capability check extension for ptp_kvm Jianyong Wu

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