[U-Boot] [PATCH 2/3] ARM: rmobile: Add basic PSCI support for r8a7790 SoC

[Marek Vasut <marek.vasut@gmail.com>]

On 2/26/19 8:37 PM, Oleksandr wrote:
> 
> Hi, Marek

Hi,

>>>>>>>> +}
>>>>>>>> +
>>>>>>>> +/*
>>>>>>>> + * Reset vector for secondary CPUs.
>>>>>>>> + * This will be mapped at address 0 by SBAR register.
>>>>>>>> + * We need _long_ jump to the physical address.
>>>>>>>> + */
>>>>>>>> +asm("    .arm\n"
>>>>>>>> +    "    .align 12\n"
>>>>>>>> +    "    .globl shmobile_boot_vector\n"
>>>>>>>> +    "shmobile_boot_vector:\n"
>>>>>>>> +    "    ldr r1, 1f\n"
>>>>>>>> +    "    bx    r1\n"
>>>>>>>> +    "    .type shmobile_boot_vector, %function\n"
>>>>>>>> +    "    .size shmobile_boot_vector, .-shmobile_boot_vector\n"
>>>>>>>> +    "    .align    2\n"
>>>>>>>> +    "    .globl    shmobile_boot_fn\n"
>>>>>>>> +    "shmobile_boot_fn:\n"
>>>>>>>> +    "1:    .space    4\n"
>>>>>>>> +    "    .globl    shmobile_boot_size\n"
>>>>>>>> +    "shmobile_boot_size:\n"
>>>>>>>> +    "    .long    .-shmobile_boot_vector\n");
>>>>>>> Why can't this be implemented in C ?
>>>>>> This "reset vector" code was ported from Linux:
>>>>>>
>>>>>> https://elixir.bootlin.com/linux/v5.0-rc5/source/arch/arm/mach-shmobile/headsmp.S#L21
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Really don't know whether it can be implemented in C.
>>>>>>
>>>>>> I was thinking of moving this code to a separate ASM file in order
>>>>>> not
>>>>>> to mix C and ASM. What do you think about it?
>>>>> U-Boot already has a reset vector code, can't that be reused ?
>>>> I don't think. Being honest, I couldn't find an obvious way how to
>>>> reuse
>>>> (I assume you meant arch/arm/cpu/armv7/start.S).
>>> Maybe it needs some additional work first ?
>>> It seems Altera socfpga somehow uses the U-Boot reset vectors for PSCI,
>>> so it should at least be possible.
>>
>> Could you, please, point me in code? Unfortunately, I wasn't able to
>> find.
>>
>>
>>>
>>>> The newly turned on secondary CPU entry should be common
>>>> "psci_cpu_entry", which does proper things.
>>>>
>>>> And this reset vector is just "a small piece of code" to be located in
>>>> on-chip RAM (with limited size) and used for the jump stub...
>>> We already have the SPL reset vectors in SRAM, maybe that can be
>>> recycled somehow ?
>>
>>
>> The only idea I have, how it may be recycled (not sure whether it will
>> work...)
>>
>>
>> diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
>> index 0cb6dd39cc..69acf4677b 100644
>> --- a/arch/arm/cpu/armv7/start.S
>> +++ b/arch/arm/cpu/armv7/start.S
>> @@ -36,6 +36,12 @@
>>  #endif
>>
>>  reset:
>> +
>> +#if defined(CONFIG_ARMV7_PSCI) && !defined(CONFIG_SPL_BUILD)
>> +       b psci_cpu_entry_jump
>> +       /* return only if this is not "a newly turned on CPU" using
>> PSCI) */
>> +#endif
>> +
>>         /* Allow the board to save important registers */
>>         b       save_boot_params
>>  save_boot_params_ret:
>> @@ -128,6 +134,21 @@ ENDPROC(switch_to_hypervisor)
>>         .weak   switch_to_hypervisor
>>  #endif
>>
>> +/*
>> + * Each platform which implements psci_cpu_entry_jump function should
>> perform
>> + * in the following way:
>> + *
>> + * If the executing this call CPU is exactly that CPU we are
>> expecting to be
>> + * powered on, then jump to psci_cpu_entry and never return.
>> + * Otherwise return to the caller.
>> + */
>> +#if defined(CONFIG_ARMV7_PSCI) && !defined(CONFIG_SPL_BUILD)
>> +ENTRY(psci_cpu_entry_jump)
>> +       movs    pc, lr
>> +ENDPROC(psci_cpu_entry_jump)
>> +.weak psci_cpu_entry_jump
>> +#endif
>> +
>>  /*************************************************************************
>>
>>   *
>>   * cpu_init_cp15
>>
>>
>> What do you think?
>>
>>
>> It would be much appreciated, if you could provide some hints.
> 
> 
> Don't want to be annoying, but it would be really nice to get my
> questions answered...

I am sorry, I am too busy right now. I will answer that once I can
properly study the problem and give you a useful answer.

-- 
Best regards,
Marek Vasut