From: "Richard W.M. Jones" <rjones@redhat.com>
To: Anup Patel <Anup.Patel@wdc.com>
Cc: "qemu-riscv@nongnu.org" <qemu-riscv@nongnu.org>,
Sagar Karandikar <sagark@eecs.berkeley.edu>,
Bastian Koppelmann <kbastian@mail.uni-paderborn.de>,
Palmer Dabbelt <palmer@sifive.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
Atish Patra <Atish.Patra@wdc.com>,
Alistair Francis <Alistair.Francis@wdc.com>,
Anup Patel <anup@brainfault.org>
Subject: Re: [PATCH 0/2] RTC support for QEMU RISC-V virt machine
Date: Fri, 27 Sep 2019 13:30:47 +0100 [thread overview]
Message-ID: <20190927123047.GO3888@redhat.com> (raw)
In-Reply-To: <MN2PR04MB6061BA18651453F590A1CE738D810@MN2PR04MB6061.namprd04.prod.outlook.com>
On Fri, Sep 27, 2019 at 12:05:43PM +0000, Anup Patel wrote:
>
>
> > -----Original Message-----
> > From: Richard W.M. Jones <rjones@redhat.com>
> > Sent: Friday, September 27, 2019 5:21 PM
> > To: Anup Patel <Anup.Patel@wdc.com>
> > Cc: Palmer Dabbelt <palmer@sifive.com>; Alistair Francis
> > <Alistair.Francis@wdc.com>; Sagar Karandikar <sagark@eecs.berkeley.edu>;
> > Bastian Koppelmann <kbastian@mail.uni-paderborn.de>; Atish Patra
> > <Atish.Patra@wdc.com>; qemu-riscv@nongnu.org; qemu-
> > devel@nongnu.org; Anup Patel <anup@brainfault.org>
> > Subject: Re: [PATCH 0/2] RTC support for QEMU RISC-V virt machine
> >
> >
> > On Tue, Sep 24, 2019 at 08:42:36AM +0000, Anup Patel wrote:
> > > This series adds RTC device to QEMU RISC-V virt machine. We have
> > > selected Goldfish RTC device model for this. It's a pretty simple
> > > synthetic device with few MMIO registers and no dependency external
> > > clock. The driver for Goldfish RTC is already available in Linux so we
> > > just need to enable it in Kconfig for RISCV and also update Linux
> > > defconfigs.
> > >
> > > We have tested this series with Linux-5.3 plus defconfig changes
> > > available in 'goldfish_rtc_v1' branch of:
> > > https://github.com/avpatel/linux.git
> >
> > Why was this device chosen instead of kvm-clock?
>
> We need a RTC device which worked fine in TCG mode (even without
> KVM). The KVMCLOCK is PTP clock which depends on KVM hypercalls.
>
> On ARM virt machine, we have PL031 so instead of that we have
> Goldfish RTC on RISC-V virt machine.
Could we not make kvm-clock work on TCG (I wasn't aware that it needed
actual KVM - I wonder how timekeeping works on TCG?)
Alternately why not use PL031 here?
The reason I'm asking this is because adding a new virtual device
means we have to change this all the way up the stack (libvirt,
virt-*) _and_ have special cases everywhere just for RISC-V. That's a
load of extra work for everyone.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html
next prev parent reply other threads:[~2019-09-27 13:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-24 8:42 [PATCH 0/2] RTC support for QEMU RISC-V virt machine Anup Patel
2019-09-24 8:42 ` [PATCH 1/2] hw: timer: Add Goldfish RTC device Anup Patel
2019-09-24 9:50 ` Peter Maydell
2019-09-24 11:17 ` Anup Patel
2019-09-24 11:31 ` Peter Maydell
2019-09-24 12:18 ` Anup Patel
2019-09-24 8:43 ` [PATCH 2/2] riscv: virt: Use " Anup Patel
2019-09-27 11:50 ` [PATCH 0/2] RTC support for QEMU RISC-V virt machine Richard W.M. Jones
2019-09-27 12:05 ` Anup Patel
2019-09-27 12:30 ` Richard W.M. Jones [this message]
2019-09-27 12:39 ` Anup Patel
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