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SubjectRe: [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

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