Re: [Qemu-ppc] [PATCH v2 6/6] PPC 85xx: Find CPU speed on ppce500 from device tree

[Scott Wood]

On Fri, 2014-01-31 at 12:16 +0100, Alexander Graf wrote:
> The only thing we know in our PV machine through device tree is the clock
> speed of the CPUs. Take that as CPU speed, system speed and ddr speed so that
> we have some meaningful values there at all.
> 
> The CPU speed is important because our timing loops get determined based on 
> it.
> 
> Signed-off-by: Alexander Graf <address@hidden>
> ---
>  arch/powerpc/cpu/mpc85xx/Makefile           |    2 ++
>  board/freescale/qemu-ppce500/qemu-ppce500.c |   43 
> +++++++++++++++++++++++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/arch/powerpc/cpu/mpc85xx/Makefile 
> b/arch/powerpc/cpu/mpc85xx/Makefile
> index ef7637a..4094785 100644
> --- a/arch/powerpc/cpu/mpc85xx/Makefile
> +++ b/arch/powerpc/cpu/mpc85xx/Makefile
> @@ -102,7 +102,9 @@ obj-y     += cpu.o
>  obj-y        += cpu_init.o
>  obj-y        += cpu_init_early.o
>  obj-y        += interrupts.o
> +ifneq ($(CONFIG_QEMU_E500),y)
>  obj-y        += speed.o
> +endif
>  obj-y        += tlb.o
>  obj-y        += traps.o
>  
> diff --git a/board/freescale/qemu-ppce500/qemu-ppce500.c 
> b/board/freescale/qemu-ppce500/qemu-ppce500.c
> index 5d4dd64..9e9d688 100644
> --- a/board/freescale/qemu-ppce500/qemu-ppce500.c
> +++ b/board/freescale/qemu-ppce500/qemu-ppce500.c
> @@ -407,3 +407,46 @@ void init_laws(void)
>  {
>       /* We don't emulate LAWs yet */
>  }
> +
> +static uint32_t get_cpu_freq(void)
> +{
> +     const void *fdt = get_fdt();
> +     int cpus_node = fdt_path_offset(fdt, "/cpus");
> +     int cpu_node = fdt_first_subnode(fdt, cpus_node);
> +     return myfdt_one_cell(fdt, cpu_node, "clock-frequency", 0);
> +}
> +
> +void get_sys_info(sys_info_t *sys_info)
> +{
> +     int freq = get_cpu_freq();
> +
> +     memset(sys_info, 0, sizeof(sys_info_t));
> +     sys_info->freq_systembus = freq;
> +     sys_info->freq_ddrbus = freq;
> +     sys_info->freq_processor[0] = freq;
> +}
> +
> +int get_clocks (void)
> +{
> +     sys_info_t sys_info;
> +
> +     get_sys_info(&sys_info);
> +
> +     gd->cpu_clk = sys_info.freq_processor[0];
> +     gd->bus_clk = sys_info.freq_systembus;
> +     gd->mem_clk = sys_info.freq_ddrbus;
> +     gd->arch.lbc_clk = sys_info.freq_ddrbus;
> +
> +     return 0;
> +}

This probably decreases the accuracy of the timebase frequency, since
you'll be basing it on the CPU frequency rather than the bus frequency.

If you're doing this, why not override get_tbclk() as well?

-Scott