[U-Boot] [PATCH] efi_loader: allow efi_loader code to call EFI interfaces

[Alexander Graf]

On 25.07.17 01:47, Rob Clark wrote:
> To implement efi_load_image() for the case of loading an image from a
> device path rather than image already loaded into source_buffer, it is
> convenient to be able to re-use simple-file-system and efi-file
> interfaces.  But these are already using EFI_ENTER()/EFI_EXIT().  Allow
> entry into EFI interfaces to be recursive, since this greatly simplifies
> things.
> 
> (And hypothetically this would be needed anyways to allow grub to call
> into interfaces installed by something outside of grub.)
> 
> Signed-off-by: Rob Clark <robdclark at gmail.com>

So there are 2 ways to do this:

   1) Keep a refcount, only transition when passing the 0 level
   2) Explicitly split functions with ENTRY/EXIT from their core functions

So far we used approach 2, splitting functions that are used by both 
internal and external code into _ext (for externally called) and normal 
functions. You can see this pattern quite a few times throughout efi_loader.

I definitely did try the refcount approach back when I decided for 
approach 2 and it failed on me in some case, but I can't remember where.

Either way, we should definitely be consistent. Either we always use 
refcounting or we shouldn't bother with it. So if you can make a version 
work where all _ext variants disappear and we're magically reentrant, 
I'll be happy to take that. I'm fairly sure it'll break somewhere though :).


Alex

> ---
>   lib/efi_loader/efi_boottime.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
> index 8735b1f418..a113124708 100644
> --- a/lib/efi_loader/efi_boottime.c
> +++ b/lib/efi_loader/efi_boottime.c
> @@ -47,6 +47,7 @@ static struct efi_configuration_table __efi_runtime_data efi_conf_table[2];
>    * EFI callback entry/exit.
>    */
>   static volatile void *efi_gd, *app_gd;
> +static int entry_level = 0;
>   #endif
>   
>   /* Called from do_bootefi_exec() */
> @@ -61,6 +62,8 @@ void efi_save_gd(void)
>   void efi_restore_gd(void)
>   {
>   #ifdef CONFIG_ARM
> +	if (entry_level++)
> +		return;
>   	/* Only restore if we're already in EFI context */
>   	if (!efi_gd)
>   		return;
> @@ -75,6 +78,8 @@ void efi_restore_gd(void)
>   efi_status_t efi_exit_func(efi_status_t ret)
>   {
>   #ifdef CONFIG_ARM
> +	if (--entry_level)
> +		return ret;
>   	gd = app_gd;
>   #endif
>   
>