RE: [PATCH v15 8/9] doc: add ptp_kvm introduction for arm64 support

[Jianyong Wu <Jianyong.Wu@xxxxxxx>]

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@xxxxxxxxxx>
> Sent: Monday, November 23, 2020 6:58 PM
> To: Jianyong Wu <Jianyong.Wu@xxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; yangbo.lu@xxxxxxx; john.stultz@xxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; sean.j.christopherson@xxxxxxxxx;
> richardcochran@xxxxxxxxx; Mark Rutland <Mark.Rutland@xxxxxxx>;
> will@xxxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Andre
> Przywara <Andre.Przywara@xxxxxxx>; Steven Price
> <Steven.Price@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx; Steve Capper <Steve.Capper@xxxxxxx>; Justin He
> <Justin.He@xxxxxxx>; nd <nd@xxxxxxx>
> 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@xxxxxxx>
> > ---
> >  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

OK.

Thanks
Jianyong 
> 
>          M.
> --
> Jazz is not dead. It just smells funny...