[U-Boot] [PATCH 1/1] efi_loader: remove efi_exit_caches()

[Heinrich Schuchardt]

On 7/22/19 8:59 PM, Mark Kettenis wrote:
>> From: Heinrich Schuchardt <xypron.glpk at gmx.de>
>> Date: Sat, 20 Jul 2019 13:23:13 +0200
>>
>> On 7/20/19 1:59 AM, Jonathan Gray wrote:
>>> On Fri, Jul 19, 2019 at 08:25:45PM +0200, Heinrich Schuchardt wrote:
>>>> In GRUB before 2.04 a bug existed which did not allow booting some ARM32
>>>> boards if U-Boot did not disable caches, cf.
>>>> https://lists.linaro.org/pipermail/cross-distro/2019-July/000933.html
>>>>
>>>> In ExitBootServices() we were disabling the caches by calling
>>>> cleanup_before_linux(). This workaround is not needed anymore.
>>>
>>> It is required for at least OpenBSD, FreeBSD and NetBSD.
>>> Which are all now forced to carry patches to be able to use U-Boot.
>>
>> Please, compare function run_loadfile() in files
>> sys/arch/arm64/stand/efiboot/exec.c and
>> sys/arch/armv7/stand/efiboot/exec.c of openbsd/src.
>>
>> On arm64 after loading the kernel you flush the data and instruction
>> caches. On armv7 you don't. As the UEFI spec requires caches to be
>> switched on this is bound to fail. You should be good if you flush
>> caches like you do on arm64.
>>
>> You can find the relevant code for GRUB in
>> grub-core/kern/arm/cache.S and
>> grub-core/kern/arm/cache.c
>>
>> After GRUB loads the Linux kernel it calls
>> grub_arch_sync_caches ((void *) linux_addr, linux_size);
>> in function linux_boot().
>
> Thanks for the pointer.  I added code to OpenBSD's BOOTARM.EFI to
> disable the caches and MMU such that the kernel ends up being started
> in the same state as before.
>
> That still leaves us with the L2 cache issue though.  A U-Boot with
> CONFIG_SYS_L2CACHE_OFF set works, whereas without it doesn't.
>

I just tested on Wandboard which is an i.MX6 system with a
architecturally defined L2 cache. The operating system is Debian Buster
which has a GRUB 2.02 but where the EFI path has been patched like in
GRUB 2.04.

It will only boot via GRUB if either CONFIG_SYS_L2CACHE_OFF=y or
cleanup_before_linux() is called (in efi_exit_caches()).

As current GRUB calls StartImage() itself the original logic implemented
by Alex not to call cleanup_before_linux() if a payload has called
StartImage() does not work.

@Alex:
Given this finding and the discussion in this thread could you, please,
revisit your review comment in
https://lists.denx.de/pipermail/u-boot/2019-July/377339.html
[RFC 1/1] efi_loader: usage of cleanup_before_linux()

I think short term we should always call cleanup_before_linux() and long
term we should move to a logic switching of only architecturally defined
caches in efi_init_obj_list(), i.e. before loading any EFI binary.

Best regards

Heinrich