netdev - Re: [RFC PATCH v12 10/11] arm64: add mechanism to let user choose which counter to return

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Date:   Sat, 23 May 2020 18:47:21 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Jianyong Wu <jianyong.wu@....com>
Cc:     netdev@...r.kernel.org, yangbo.lu@....com, john.stultz@...aro.org,
        tglx@...utronix.de, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, maz@...nel.org,
        Mark.Rutland@....com, will@...nel.org, suzuki.poulose@....com,
        steven.price@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, Steve.Capper@....com, Kaly.Xin@....com,
        justin.he@....com, Wei.Chen@....com, nd@....com
Subject: Re: [RFC PATCH v12 10/11] arm64: add mechanism to let user choose
 which counter to return

On Fri, May 22, 2020 at 04:37:23PM +0800, Jianyong Wu wrote:

> To use this feature, you should call PTP_EXTTS_REQUEST(2) ioctl with flag
> set bit PTP_KVM_ARM_PHY_COUNTER in its argument then call
> PTP_SYS_OFFSET_PRECISE(2) ioctl to get the cross timestamp and phyical
> counter will return. If the bit not set or no call for PTP_EXTTS_REQUEST2,
> virtual counter will return by default.

I'm sorry, but NAK on this completely bizarre twisting of the user
space API.

> 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;
> +#endif
>  	switch (cmd) {
>  
>  	case PTP_CLOCK_GETCAPS:
> @@ -149,6 +152,24 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
>  			err = -EFAULT;
>  			break;
>  		}
> +
> +#ifdef CONFIG_ARM64
> +		/*
> +		 * Just using this ioctl to tell kvm ptp driver to get PHC
> +		 * with physical counter, so if bit PTP_KVM_ARM_PHY_COUNTER
> +		 * is set then just exit directly.
> +		 * 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.
> +		 * This is only for arm64.
> +		 */
> +		if (req.extts.flags & PTP_KVM_ARM_PHY_COUNTER) {
> +			flag = 1;
> +			break;
> +		}
> +#endif

This file contains the generic PTP Hardware Clock character device
implementation.  It is no place for platform specific hacks.

Sorry,
Richard