linux-kernel - Re: [PATCH v15 8/9] doc: add ptp_kvm introduction for arm64 support

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Message-ID: <38fad448a3a465e4c35994ce61f4d8dd@kernel.org>
Date:   Mon, 23 Nov 2020 10:58:07 +0000
From:   Marc Zyngier <maz@...nel.org>
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, richardcochran@...il.com,
        Mark.Rutland@....com, will@...nel.org, suzuki.poulose@....com,
        Andre.Przywara@....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, justin.he@....com, nd@....com
Subject: Re: [PATCH v15 8/9] doc: add ptp_kvm introduction for arm64 support

On 2020-11-11 06:22, Jianyong Wu wrote:
> PTP_KVM implementation depends on hypercall using SMCCC. So we
> introduce a new SMCCC service ID. This doc explains how does the
> ID define and how does PTP_KVM works on arm/arm64.
> 
> Signed-off-by: Jianyong Wu <jianyong.wu@....com>
> ---
>  Documentation/virt/kvm/api.rst         |  9 +++++++
>  Documentation/virt/kvm/arm/index.rst   |  1 +
>  Documentation/virt/kvm/arm/ptp_kvm.rst | 29 +++++++++++++++++++++
>  Documentation/virt/kvm/timekeeping.rst | 35 ++++++++++++++++++++++++++
>  4 files changed, 74 insertions(+)
>  create mode 100644 Documentation/virt/kvm/arm/ptp_kvm.rst
> 
> diff --git a/Documentation/virt/kvm/api.rst 
> b/Documentation/virt/kvm/api.rst
> index 36d5f1f3c6dd..9843dbcbf770 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6391,3 +6391,12 @@ When enabled, KVM will disable paravirtual
> features provided to the
>  guest according to the bits in the KVM_CPUID_FEATURES CPUID leaf
>  (0x40000001). Otherwise, a guest may use the paravirtual features
>  regardless of what has actually been exposed through the CPUID leaf.
> +
> +8.27 KVM_CAP_PTP_KVM
> +--------------------
> +
> +:Architectures: arm64
> +
> +This capability indicates that KVM virtual PTP service is supported in 
> host.
> +It must company with the implementation of KVM virtual PTP service in 
> host
> +so VMM can probe if there is the service in host by checking this 
> capability.
> diff --git a/Documentation/virt/kvm/arm/index.rst
> b/Documentation/virt/kvm/arm/index.rst
> index 3e2b2aba90fc..78a9b670aafe 100644
> --- a/Documentation/virt/kvm/arm/index.rst
> +++ b/Documentation/virt/kvm/arm/index.rst
> @@ -10,3 +10,4 @@ ARM
>     hyp-abi
>     psci
>     pvtime
> +   ptp_kvm
> diff --git a/Documentation/virt/kvm/arm/ptp_kvm.rst
> b/Documentation/virt/kvm/arm/ptp_kvm.rst
> new file mode 100644
> index 000000000000..bb1e6cfefe44
> --- /dev/null
> +++ b/Documentation/virt/kvm/arm/ptp_kvm.rst
> @@ -0,0 +1,29 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +PTP_KVM support for arm/arm64
> +=============================
> +
> +PTP_KVM is used for time sync between guest and host in a high 
> precision.
> +It needs to get the wall time and counter value from the host and
> transfer these
> +to guest via hypercall service. So one more hypercall service has been 
> added.
> +
> +This new SMCCC hypercall is defined as:
> +
> +* ARM_SMCCC_HYP_KVM_PTP_FUNC_ID: 0x86000001
> +
> +As both 32 and 64-bits ptp_kvm client should be supported, we choose
> SMC32/HVC32
> +calling convention.
> +
> +ARM_SMCCC_HYP_KVM_PTP_FUNC_ID:
> +
> +    =============    ==========    ==========
> +    Function ID:     (uint32)      0x86000001
> +    Arguments:	     (uint32)      ARM_PTP_PHY_COUNTER(1) or
> ARM_PTP_VIRT_COUNTER(0)
> +                                   which indicate acquiring physical 
> counter or
> +                                   virtual counter respectively.
> +    return value:    (uint32)      NOT_SUPPORTED(-1) or val0 and val1 
> represent
> +                                   wall clock time and val2 and val3 
> represent
> +                                   counter cycle.

This needs a lot more description:

- Which word contains what part of the data (upper/lower part of the 
64bit data)
- The endianness of the data returned

         M.
-- 
Jazz is not dead. It just smells funny...