[U-Boot] [PATCH 3/5] Allow arch-specific setting of global_data in board_init_f_mem()

[Bin Meng]

Hi Simon,

On Mon, Aug 3, 2015 at 8:10 AM, Simon Glass <sjg at chromium.org> wrote:
> At present we have a simple assignment to gd. With some archs this is
> implemented as a register or through some other means; a simple assignment
> does not suit in all cases.
>
> Change this to a function and add documentation to describe how this all
> works.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
>  common/board_f.c | 14 +++++++++++---
>  include/common.h | 40 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 51 insertions(+), 3 deletions(-)
>
> diff --git a/common/board_f.c b/common/board_f.c
> index a947770..3d1f305 100644
> --- a/common/board_f.c
> +++ b/common/board_f.c
> @@ -1024,15 +1024,23 @@ void board_init_f_r(void)
>  #endif /* CONFIG_X86 */
>
>  #ifndef CONFIG_X86
> -ulong board_init_f_mem(ulong top)
> +__weak void arch_setup_gdt(struct global_data *gd_ptr)
>  {
> +       gd = gd_ptr;
> +}
> +
> +ulong board_init_f_mem(ulong top, ulong reserve_size)

What is reserve_size? I don't see it is used by this function. If we
change the signature, we need also update arc and ppc4xx start.S
otherwise they will break.

> +{
> +       struct global_data *gd_ptr;
> +
>         /* Leave space for the stack we are running with now */
>         top -= 0x40;
>
>         top -= sizeof(struct global_data);
>         top = ALIGN(top, 16);
> -       gd = (struct global_data *)top;
> -       memset((void *)gd, '\0', sizeof(*gd));
> +       gd_ptr = (struct global_data *)top;
> +       memset(gd_ptr, '\0', sizeof(*gd));
> +       arch_setup_gdt(gd_ptr);

gdt? Should be just arch_setup_gd()?

>
>  #ifdef CONFIG_SYS_MALLOC_F_LEN
>         top -= CONFIG_SYS_MALLOC_F_LEN;
> diff --git a/include/common.h b/include/common.h
> index fcc9ae7..029eb1f 100644
> --- a/include/common.h
> +++ b/include/common.h
> @@ -217,6 +217,46 @@ extern char console_buffer[];
>  /* arch/$(ARCH)/lib/board.c */
>  void board_init_f(ulong);
>  void board_init_r(gd_t *, ulong) __attribute__ ((noreturn));
> +
> +/**
> + * board_init_f_mem() - Allocate global data and set stack position
> + *
> + * This function is called by each architecture very early in the start-up
> + * code to set up the environment for board_init_f(). It allocates space for
> + * global_data (see include/asm-generic/global_data.h) and places the stack
> + * below this.
> + *
> + * This function requires a stack[1] Normally this is at @top. The function
> + * starts allocating space from 64 bytes below @top. First it creates space
> + * for global_data. then it calls arch_setup_gd() which sets gd to point to

Nits: . -> ,

> + * the global_data space and can reserve additional bytes of space if
> + * required). Finally it allocates early malloc() memory
> + * (CONFIG_SYS_MALLOC_F_LEN). The new top of the stack is just below this,
> + * and it returned by this function.
> + *
> + * [1] Strictly speaking it would be possible to implement this function
> + * in C on many archs such that it does not require a stack. However this
> + * does not seem hugely important as only 64 byte are wasted.

Where is the 64 bytes it uses? I only see a variable gd_ptr on the stack.

> + *
> + * @top:       Top of available memory, also normally the top of the stack
> + * @return:    New stack location
> + */
> +ulong board_init_f_mem(ulong top, ulong reserve_size);

I don't like the name board_init_f_mem(). It actually does two things:
creates global data pointer and reserve the early malloc() memory
size. Also it looks like it's more like an arch thing instead of a
board's. How about setup_gd_f_mem()?

> +
> +/**
> + * arch_setup_gdt() - Set up the global_data pointer
> + *
> + * This pointer is special in some architectures and cannot easily be assigned
> + * to. For example on x86 it is implemented by adding a specific record to its
> + * Global Descriptor Table! So we we provide a function to carry out this task.
> + * For most architectures this can simply be:
> + *
> + *    gd = gd_ptr;
> + *
> + * @gd_ptr:    Pointer to global data
> + */
> +void arch_setup_gdt(gd_t *gd_ptr);
> +
>  int checkboard(void);
>  int show_board_info(void);
>  int checkflash(void);
> --

Regards,
Bin