[U-Boot] [PATCH 04/24] armv8: add lowlevel_init.S

[Andre Przywara]

Hi Alex,

thanks for having a look!

On 21/11/16 15:34, Alexander Graf wrote:
> 
> 
> On 20/11/2016 15:56, Andre Przywara wrote:
>> For boards that call s_init() when the SPL runs, we are expected to
>> setup an early stack before calling this C function.
>> Implement the proper AArch64 version of this based on the ARMv7 code.
>> This allows sunxi boards to setup the basic peripherals even on with a
>> 64-bit SPL.
>>
>> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> 
> Isn't that what _main in ./arch/arm/lib/crt0_64.S is supposed to do?
> That should be used for the SPL flow too, no?

I saw that too, but apparently this one here is a some shortcut for the
SPL. TBH I didn't dare to look too closely, as this seems to be a bit
entangled.

....

>> ---
>>  arch/arm/cpu/armv8/Makefile        |  1 +
>>  arch/arm/cpu/armv8/lowlevel_init.S | 44
>> ++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 45 insertions(+)
>>  create mode 100644 arch/arm/cpu/armv8/lowlevel_init.S
>>
>> diff --git a/arch/arm/cpu/armv8/Makefile b/arch/arm/cpu/armv8/Makefile
>> index dea1465..799a752 100644
>> --- a/arch/arm/cpu/armv8/Makefile
>> +++ b/arch/arm/cpu/armv8/Makefile
>> @@ -25,3 +25,4 @@ obj-$(CONFIG_FSL_LAYERSCAPE) += fsl-layerscape/
>>  obj-$(CONFIG_S32V234) += s32v234/
>>  obj-$(CONFIG_ARCH_ZYNQMP) += zynqmp/
>>  obj-$(CONFIG_TARGET_HIKEY) += hisilicon/
>> +obj-$(CONFIG_ARCH_SUNXI) += lowlevel_init.o
>> diff --git a/arch/arm/cpu/armv8/lowlevel_init.S
>> b/arch/arm/cpu/armv8/lowlevel_init.S
>> new file mode 100644
>> index 0000000..189e35f
>> --- /dev/null
>> +++ b/arch/arm/cpu/armv8/lowlevel_init.S
>> @@ -0,0 +1,44 @@
>> +/*
>> + * A lowlevel_init function that sets up the stack to call a C
>> function to
>> + * perform further init.
>> + *
>> + * SPDX-License-Identifier:    GPL-2.0+
>> + */
>> +
>> +#include <asm-offsets.h>
>> +#include <config.h>
>> +#include <linux/linkage.h>
>> +
>> +ENTRY(lowlevel_init)
>> +    /*
>> +     * Setup a temporary stack. Global data is not available yet.
>> +     */
>> +#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
>> +    ldr    w0, =CONFIG_SPL_STACK
>> +#else
>> +    ldr    w0, =CONFIG_SYS_INIT_SP_ADDR
>> +#endif
>> +    bic    sp, x0, #0xf    /* 16-byte alignment for ABI compliance */
>> +
>> +    /*
>> +     * Save the old LR(passed in x29) and the current LR to stack
>> +     */
>> +    stp    x29, x30, [sp, #-16]!
>> +
>> +    /*
>> +     * Call the very early init function. This should do only the
>> +     * absolute bare minimum to get started. It should not:
>> +     *
>> +     * - set up DRAM
>> +     * - use global_data
>> +     * - clear BSS
>> +     * - try to start a console
>> +     *
>> +     * For boards with SPL this should be empty since SPL can do all of
>> +     * this init in the SPL board_init_f() function which is called
>> +     * immediately after this.
> 
> So this comment says that s_init shouldn't even be used for SPL and
> instead we should use board_init_f which is what crt0 calls.

Yes, that is a good point. So the sunxi port seemed to ignore this
recommendation and do it in its own way (TM).
Frankly I didn't want to fix this one too at this point, so I just went
ahead with filling the 64-bit gaps.
But I agree that this should be fixed eventually. The line above:
+obj-$(CONFIG_ARCH_SUNXI) += lowlevel_init.o
hints already that something is not really right here, as SUNXI is the
only user of this rather generic function.
If I find some spare time (haha), I might take a look, otherwise: be my
guest ;-)

Cheers,
Andre.