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

[Scott Wood]

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?

-Scott