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

Jianyong Wu
2020-11-24T05:22:27Z

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Monday, November 23, 2020 6:58 PM
> To: Jianyong Wu <Jianyong.Wu@arm.com>
> Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>;
> will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Andre
> Przywara <Andre.Przywara@arm.com>; Steven Price
> <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
> kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Justin He
> <Justin.He@arm.com>; nd <nd@arm.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@arm.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

OK.

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