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

[Alexander Graf]

On 04.02.2014, at 03:52, Scott Wood <address@hidden> wrote:

> 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?

That one only uses variables I already control, no?

unsigned long get_tbclk (void)
{
        unsigned long tbclk_div = CONFIG_SYS_FSL_TBCLK_DIV;

        return (gd->bus_clk + (tbclk_div >> 1)) / tbclk_div;
}


Alex