linux-kernel - Re: [RFC PATCH v3 6/7] virtio_rtc: Add Arm Generic Timer cross-timestamping

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Date: Sat, 15 Jun 2024 08:50:53 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Peter Hilber <peter.hilber@...nsynergy.com>,
 linux-kernel@...r.kernel.org,  virtualization@...ts.linux.dev,
 virtio-dev@...ts.oasis-open.org,  linux-arm-kernel@...ts.infradead.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
  Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Marc Zyngier <maz@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Daniel Lezcano
 <daniel.lezcano@...aro.org>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH v3 6/7] virtio_rtc: Add Arm Generic Timer
 cross-timestamping

On Mon, 2023-12-18 at 08:38 +0100, Peter Hilber wrote:
> 
> +int viortc_hw_xtstamp_params(u16 *hw_counter, enum clocksource_ids *cs_id)
> +{
> +       *hw_counter = VIRTIO_RTC_COUNTER_ARM_VIRT;

Hm, but what if it isn't? I think you need to put this in
drivers/clocksource/arm_arch_timer.c where it can do something like
kvm_arch_ptp_get_crosststamp() does to decide:

        if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
                ptp_counter = KVM_PTP_VIRT_COUNTER;
        else
                ptp_counter = KVM_PTP_PHYS_COUNTER;

> +       *cs_id = CSID_ARM_ARCH_COUNTER;
> +
> +       return 0;
> +}

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