Re: [Qemu-devel] [PATCH] riscv: virt: Add cpu-topology DT node.

From: "Daniel P. Berrangé" <berrange@redhat.com>
To: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Thomas Huth <thuth@redhat.com>,
	"open list:RISC-V" <qemu-riscv@nongnu.org>,
	Sagar Karandikar <sagark@eecs.berkeley.edu>,
	Bastian Koppelmann <kbastian@mail.uni-paderborn.de>,
	Palmer Dabbelt <palmer@sifive.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	"qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>,
	Atish Patra <atish.patra@wdc.com>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Alistair Francis <alistair23@gmail.com>
Subject: Re: [Qemu-devel] [PATCH] riscv: virt: Add cpu-topology DT node.
Date: Tue, 25 Jun 2019 11:41:22 +0100	[thread overview]
Message-ID: <20190625104122.GC3139@redhat.com> (raw)
In-Reply-To: <09df5e02-e241-1046-5051-909c53fe19b7@redhat.com>

On Tue, Jun 25, 2019 at 12:36:35PM +0200, Philippe Mathieu-Daudé wrote:
> On 6/25/19 1:24 AM, Alistair Francis wrote:
> > On Mon, Jun 24, 2019 at 3:57 PM Atish Patra <atish.patra@wdc.com> wrote:
> >>
> >> Currently, there is no cpu topology defined in RISC-V.
> >> Define a device tree node that clearly describes the
> >> entire topology. This saves the trouble of scanning individual
> >> cache to figure out the topology.
> >>
> >> Here is the linux kernel patch series that enables topology
> >> for RISC-V.
> >>
> >> http://lists.infradead.org/pipermail/linux-riscv/2019-June/005072.html
> >>
> >> CPU topology after applying this patch in QEMU & above series in kernel
> >>
> >> / # cat /sys/devices/system/cpu/cpu2/topology/thread_siblings_list
> >> 2
> >> / # cat /sys/devices/system/cpu/cpu2/topology/physical_package_id
> >> 0
> >> / # cat /sys/devices/system/cpu/cpu2/topology/core_siblings_list
> >> 0-7
> >>
> >> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> >> ---
> >>  hw/riscv/virt.c | 21 +++++++++++++++++++--
> >>  1 file changed, 19 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> >> index 84d94d0c42d8..da0b8aa18747 100644
> >> --- a/hw/riscv/virt.c
> >> +++ b/hw/riscv/virt.c
> >> @@ -203,9 +203,12 @@ static void *create_fdt(RISCVVirtState *s, const struct MemmapEntry *memmap,
> >>          qemu_fdt_setprop_string(fdt, nodename, "status", "okay");
> >>          qemu_fdt_setprop_cell(fdt, nodename, "reg", cpu);
> >>          qemu_fdt_setprop_string(fdt, nodename, "device_type", "cpu");
> >> +        qemu_fdt_setprop_cell(fdt, nodename, "phandle", cpu_phandle);
> >> +        qemu_fdt_setprop_cell(fdt, nodename, "linux,phandle", cpu_phandle);
> >> +        int intc_phandle = phandle++;
> > 
> > Don't declare variables in the middle of code. The variable must be
> > declared at the start of a block.
> 
> I guess this has been relaxed since we allow GNU C99:

Even though we allow GNU C99 I think it is undesirable to declare variables
in the middle of methods. This is especially true when combined with "goto"
as you end up with undefined / uninitialized vairable contents at the jump
target, if we've jumped over the variable declaration.

We can't enforce location of variable declarations, but I'd really
recommend we keep them all at the start of code blocks.

Regards,
Daniel
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