[U-Boot] ARM64: How to protect spin-table code from U-Boot?

[Masahiro Yamada]

Hi Alex,


2016-05-07 20:30 GMT+09:00 Alexander Graf <agraf at suse.de>:
>
>
> On 07.05.16 09:12, Masahiro Yamada wrote:
>> Hi.
>>
>> I assume the following code in
>> arch/arm/cpu/armv8/start.S is for spin-table.
>>
>>
>>
>> #ifdef CONFIG_ARMV8_MULTIENTRY
>>        branch_if_master x0, x1, master_cpu
>>
>>        /*
>>         * Slave CPUs
>>         */
>> slave_cpu:
>>        wfe
>>        ldr x1, =CPU_RELEASE_ADDR
>>        ldr x0, [x1]
>>        cbz x0, slave_cpu
>>        br x0 /* branch to the given address */
>> master_cpu:
>>        /* On the master CPU */
>> #endif /* CONFIG_ARMV8_MULTIENTRY */
>>
>>
>>
>> As Documentation/arm64/booting.txt of Linux says,
>> slave CPUs should spin outside of the kernel in a
>> reserved area of memory.
>>
>> U-Boot generally works on DRAM, so the code for spin-table
>> should be reserved in Device Tree.
>>
>> Otherwise, the code above and the variable "CPU_RELEASE_ADDR"
>> has been destroyed by the kernel by the time slave CPUs are kicked.
>>
>> Now, I locally work-around this problem by pre-fetching necessary code
>> to the I-cache, but this solution is unstable.
>>
>>
>> My question is, is there a solution to protect spin-table code already?
>> (or on-going work to solve the problem?)
>>
>> One problem specific for U-Boot is that,
>> U-Boot relocates itself to the tail of DRAM.
>> So, it is difficult to reserve the code statically at the compile time of DT.
>
> I assume your SoC has working EL3? If so, why don't you just provide the
> respective PSCI cpu wakeup calls via ATF instead of using spin tables?
>


I am planning to switch to ARM Trusted Firmware in the future,
but there are several things to study before staring to use it.
(and I guess there are SoC-specific parts that should be implemented in ATF)

I needed to bring-up my first ARMv8 SoC quickly.
I am familiar with U-Boot already, so I chose to use U-Boot alone
in my early development phase.

A good thing about spin-table is that it is really simple.

Moreover, if we have something, it should be correct.
(or should be deleted if it is not working.)
I do not like the half-way house like "we implemented it, but not working".

If nobody has taken care about it yet, I am happy to work on it.
Any comment is very appreciated, of course.


-- 
Best Regards
Masahiro Yamada