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

[Alexander Graf]

On 07.02.2014, at 02:33, Scott Wood <address@hidden> wrote:

> On Thu, 2014-02-06 at 12:11 +0100, Alexander Graf wrote:
>> 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;
>> }
> 
> What did you set CONFIG_SYS_FSL_TBCLK_DIV to?

Nothing which is why it's defaulting to 8.


Alex