RE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.

From: "Jianyong Wu (Arm Technology China)" <Jianyong.Wu@arm.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"yangbo.lu@nxp.com" <yangbo.lu@nxp.com>,
	"john.stultz@linaro.org" <john.stultz@linaro.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"sean.j.christopherson@intel.com"
	<sean.j.christopherson@intel.com>,
	"maz@kernel.org" <maz@kernel.org>,
	"richardcochran@gmail.com" <richardcochran@gmail.com>,
	Mark Rutland <Mark.Rutland@arm.com>,
	Will Deacon <Will.Deacon@arm.com>,
	Suzuki Poulose <Suzuki.Poulose@arm.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Steve Capper <Steve.Capper@arm.com>,
	"Kaly Xin (Arm Technology China)" <Kaly.Xin@arm.com>,
	"Justin He (Arm Technology China)" <Justin.He@arm.com>,
	nd <nd@arm.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: RE: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
Date: Wed, 25 Sep 2019 10:27:58 +0000	[thread overview]
Message-ID: <HE1PR0801MB1676F76AE58C379A9E9006C0F4870@HE1PR0801MB1676.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <06264d8a-b9c0-5f19-db2c-6190976a2a05@redhat.com>

Hi Paolo,

> -----Original Message-----
> From: Paolo Bonzini <pbonzini@redhat.com>
> Sent: Tuesday, September 24, 2019 10:20 PM
> To: Jianyong Wu (Arm Technology China) <Jianyong.Wu@arm.com>;
> netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; sean.j.christopherson@intel.com; maz@kernel.org;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>; Will
> Deacon <Will.Deacon@arm.com>; Suzuki Poulose
> <Suzuki.Poulose@arm.com>
> Cc: linux-kernel@vger.kernel.org; kvm@vger.kernel.org; Steve Capper
> <Steve.Capper@arm.com>; Kaly Xin (Arm Technology China)
> <Kaly.Xin@arm.com>; Justin He (Arm Technology China)
> <Justin.He@arm.com>; nd <nd@arm.com>; linux-arm-
> kernel@lists.infradead.org
> Subject: Re: [RFC PATCH v3 4/6] psci: Add hvc call service for ptp_kvm.
> 
> On 23/09/19 06:57, Jianyong Wu (Arm Technology China) wrote:
> >> On 19/09/19 11:46, Jianyong Wu (Arm Technology China) wrote:
> >>>> On 18/09/19 11:57, Jianyong Wu (Arm Technology China) wrote:
> >>>>> Paolo Bonzini wrote:
> >>>>>> This is not Y2038-safe.  Please use ktime_get_real_ts64 instead,
> >>>>>> and split the 64-bit seconds value between val[0] and val[1].
> >>>
> >>> Val[] should be long not u32 I think, so in arm64 I can avoid that
> >>> Y2038_safe, but also need rewrite for arm32.
> >>
> >> I don't think there's anything inherently wrong with u32 val[], and
> >> as you notice it lets you reuse code between arm and arm64.  It's up
> >> to you and Marc to decide.
> >>
> > To compatible 32-bit, Integrates second value and nanosecond value as
> > a nanosecond value then split it into val[0] and val[1] and split cycle value
> into val[2] and val[3],  In this way, time will overflow at Y2262.
> > WDYT?
> 
> So if I understand correctly you'd multiply by 10^9 (or better shift by
> 30) the nanoseconds.
> 
Yeah, 
> That works, but why not provide 5 output registers?  Alternatively, take an
> address as input and write there.

It will be easy,  if I could have expanded the store room. But these code is the infrastructure for hypercall, I can't change them at my will.
I think only value but pointer can delivered by smccc_set_retval call.

> 
> Finally, on x86 we added an argument for the CLOCK_* that is being read
> (currently only CLOCK_REALTIME, but having room for extensibility in the API
> is always nice).
> 
IMO, I will be limited by the design of hypercall on arm64, I can only design my code under it. maybe it will be better sometime but for now I could just obey it.

Thanks
Jianyong  Wu

> Paolo