[v2] A collection of RISC-V cleanups and improvements

[PATCH v2 9/9] hw/riscv: virt: Set the clock-frequency

Posted by Alistair Francis 4 years, 1 month ago

From: Alistair Francis <alistair.francis@wdc.com>

As per the device tree specification let's set the clock-frequency for
the virt CPUs.

QEMU doesn't really have an exact clock, so let's just 1000000 as it's a
nice round number and matches the sifive_u CLINT_TIMEBASE_FREQ.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/472 (RISC-V virt)
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 hw/riscv/virt.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index 3af074148e..41a85cfc60 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -202,6 +202,7 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
         qemu_fdt_setprop_cell(mc->fdt, cpu_name, "reg",
             s->soc[socket].hartid_base + cpu);
         qemu_fdt_setprop_string(mc->fdt, cpu_name, "device_type", "cpu");
+        qemu_fdt_setprop_cell(mc->fdt, cpu_name, "clock-frequency", 1000000);
         riscv_socket_fdt_write_id(mc, mc->fdt, cpu_name, socket);
         qemu_fdt_setprop_cell(mc->fdt, cpu_name, "phandle", cpu_phandle);
 
-- 
2.31.1

Re: [PATCH v2 9/9] hw/riscv: virt: Set the clock-frequency

Posted by Bin Meng 4 years, 1 month ago

On Thu, Dec 16, 2021 at 12:55 PM Alistair Francis
<alistair.francis@opensource.wdc.com> wrote:
>
> From: Alistair Francis <alistair.francis@wdc.com>
>
> As per the device tree specification let's set the clock-frequency for
> the virt CPUs.
>
> QEMU doesn't really have an exact clock, so let's just 1000000 as it's a
> nice round number and matches the sifive_u CLINT_TIMEBASE_FREQ.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/472 (RISC-V virt)

I tend to think this issue is not valid, as the comment in the issue
says the value should reflect the running frequency.

Note the "clock-frequency" was once in the codes but was intentionally
removed before because it is not needed:

See commit 7ae05377b85f (" riscv: hw: Drop "clock-frequency" property
of cpu nodes")

> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> ---
>  hw/riscv/virt.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> index 3af074148e..41a85cfc60 100644
> --- a/hw/riscv/virt.c
> +++ b/hw/riscv/virt.c
> @@ -202,6 +202,7 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
>          qemu_fdt_setprop_cell(mc->fdt, cpu_name, "reg",
>              s->soc[socket].hartid_base + cpu);
>          qemu_fdt_setprop_string(mc->fdt, cpu_name, "device_type", "cpu");
> +        qemu_fdt_setprop_cell(mc->fdt, cpu_name, "clock-frequency", 1000000);
>          riscv_socket_fdt_write_id(mc, mc->fdt, cpu_name, socket);
>          qemu_fdt_setprop_cell(mc->fdt, cpu_name, "phandle", cpu_phandle);

Regards,
Bin

Re: [PATCH v2 9/9] hw/riscv: virt: Set the clock-frequency

Posted by Alistair Francis 4 years, 1 month ago

On Mon, Dec 20, 2021 at 5:52 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> On Thu, Dec 16, 2021 at 12:55 PM Alistair Francis
> <alistair.francis@opensource.wdc.com> wrote:
> >
> > From: Alistair Francis <alistair.francis@wdc.com>
> >
> > As per the device tree specification let's set the clock-frequency for
> > the virt CPUs.
> >
> > QEMU doesn't really have an exact clock, so let's just 1000000 as it's a
> > nice round number and matches the sifive_u CLINT_TIMEBASE_FREQ.
> >
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/472 (RISC-V virt)
>
> I tend to think this issue is not valid, as the comment in the issue
> says the value should reflect the running frequency.
>
> Note the "clock-frequency" was once in the codes but was intentionally
> removed before because it is not needed:
>
> See commit 7ae05377b85f (" riscv: hw: Drop "clock-frequency" property
> of cpu nodes")

Hmmm... Good point.

But if the device tree spec says it's required then I think we should
include it. Even if it isn't super relevant for us

Alistair

>
> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > ---
> >  hw/riscv/virt.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> > index 3af074148e..41a85cfc60 100644
> > --- a/hw/riscv/virt.c
> > +++ b/hw/riscv/virt.c
> > @@ -202,6 +202,7 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
> >          qemu_fdt_setprop_cell(mc->fdt, cpu_name, "reg",
> >              s->soc[socket].hartid_base + cpu);
> >          qemu_fdt_setprop_string(mc->fdt, cpu_name, "device_type", "cpu");
> > +        qemu_fdt_setprop_cell(mc->fdt, cpu_name, "clock-frequency", 1000000);
> >          riscv_socket_fdt_write_id(mc, mc->fdt, cpu_name, socket);
> >          qemu_fdt_setprop_cell(mc->fdt, cpu_name, "phandle", cpu_phandle);
>
> Regards,
> Bin

Re: [PATCH v2 9/9] hw/riscv: virt: Set the clock-frequency

Posted by Bin Meng 4 years, 1 month ago

On Tue, Dec 21, 2021 at 2:32 PM Alistair Francis <alistair23@gmail.com> wrote:
>
> On Mon, Dec 20, 2021 at 5:52 PM Bin Meng <bmeng.cn@gmail.com> wrote:
> >
> > On Thu, Dec 16, 2021 at 12:55 PM Alistair Francis
> > <alistair.francis@opensource.wdc.com> wrote:
> > >
> > > From: Alistair Francis <alistair.francis@wdc.com>
> > >
> > > As per the device tree specification let's set the clock-frequency for
> > > the virt CPUs.
> > >
> > > QEMU doesn't really have an exact clock, so let's just 1000000 as it's a
> > > nice round number and matches the sifive_u CLINT_TIMEBASE_FREQ.
> > >
> > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/472 (RISC-V virt)
> >
> > I tend to think this issue is not valid, as the comment in the issue
> > says the value should reflect the running frequency.
> >
> > Note the "clock-frequency" was once in the codes but was intentionally
> > removed before because it is not needed:
> >
> > See commit 7ae05377b85f (" riscv: hw: Drop "clock-frequency" property
> > of cpu nodes")
>
> Hmmm... Good point.
>
> But if the device tree spec says it's required then I think we should
> include it. Even if it isn't super relevant for us

The Linux kernel upstream RISC-V DTS files also don't have
"clock-frequency" properties. I doubt there is benefit to provide one.

Regards,
Bin

Re: [PATCH v2 9/9] hw/riscv: virt: Set the clock-frequency

Posted by Peter Maydell 3 years, 11 months ago

On Tue, 21 Dec 2021 at 06:35, Alistair Francis <alistair23@gmail.com> wrote:
>
> On Mon, Dec 20, 2021 at 5:52 PM Bin Meng <bmeng.cn@gmail.com> wrote:
> >
> > On Thu, Dec 16, 2021 at 12:55 PM Alistair Francis
> > <alistair.francis@opensource.wdc.com> wrote:
> > >
> > > From: Alistair Francis <alistair.francis@wdc.com>
> > >
> > > As per the device tree specification let's set the clock-frequency for
> > > the virt CPUs.
> > >
> > > QEMU doesn't really have an exact clock, so let's just 1000000 as it's a
> > > nice round number and matches the sifive_u CLINT_TIMEBASE_FREQ.
> > >
> > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/472 (RISC-V virt)
> >
> > I tend to think this issue is not valid, as the comment in the issue
> > says the value should reflect the running frequency.
> >
> > Note the "clock-frequency" was once in the codes but was intentionally
> > removed before because it is not needed:
> >
> > See commit 7ae05377b85f (" riscv: hw: Drop "clock-frequency" property
> > of cpu nodes")
>
> Hmmm... Good point.
>
> But if the device tree spec says it's required then I think we should
> include it. Even if it isn't super relevant for us

I talked with one of the device tree spec maintainers, and he said
that the "required" note on this property in the spec is a leftover
from the spec text for PPC ePAPR, and it isn't actually required
these days. Many DTs for real-hardware Arm boards don't set the
property, and it's not marked as required in the devicetree
yaml schema for the cpu node:
https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/cpus.yaml#L63

thanks
-- PMM

Re: [PATCH v2 9/9] hw/riscv: virt: Set the clock-frequency

Posted by Anup Patel 4 years, 1 month ago

On Thu, Dec 16, 2021 at 10:31 AM Alistair Francis
<alistair.francis@opensource.wdc.com> wrote:
>
> From: Alistair Francis <alistair.francis@wdc.com>
>
> As per the device tree specification let's set the clock-frequency for
> the virt CPUs.
>
> QEMU doesn't really have an exact clock, so let's just 1000000 as it's a
> nice round number and matches the sifive_u CLINT_TIMEBASE_FREQ.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/472 (RISC-V virt)
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> ---
>  hw/riscv/virt.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> index 3af074148e..41a85cfc60 100644
> --- a/hw/riscv/virt.c
> +++ b/hw/riscv/virt.c
> @@ -202,6 +202,7 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
>          qemu_fdt_setprop_cell(mc->fdt, cpu_name, "reg",
>              s->soc[socket].hartid_base + cpu);
>          qemu_fdt_setprop_string(mc->fdt, cpu_name, "device_type", "cpu");
> +        qemu_fdt_setprop_cell(mc->fdt, cpu_name, "clock-frequency", 1000000);

Instead of hard-coding, please use the same define used for timebase-frequency
(i.e. RISCV_ACLINT_DEFAULT_TIMEBASE_FREQ)

Regards,
Anup

>          riscv_socket_fdt_write_id(mc, mc->fdt, cpu_name, socket);
>          qemu_fdt_setprop_cell(mc->fdt, cpu_name, "phandle", cpu_phandle);
>
> --
> 2.31.1
>
>