Re: Steps forward for the LoongArch UEFI bringup patch? (was: Re: [PATCH V14 11/24] LoongArch: Add boot and setup routines)

[WANG Xuerui]

On 6/3/22 17:32, Xi Ruoyao wrote:
> On Thu, 2022-06-02 at 22:09 +0800, WANG Xuerui wrote:
>
> > For this, I don't know if Huacai should really just leave those
> > modification in the downstream fork to keep the upstream Linux clean of
> > such hacks, because to some degree dealing with such notoriety is life,
> > it seems to me. I think at this point Huacai would cooperate and tweak
> > the patch to get rid of the SVAM and other nonstandard bits as much as
> > possible, and I'll help him where necessary too.
> To me any new firmware for PC-like platforms should implement UEFI.  For
> embedded platforms device tree support will be added later.
>
> For those guys impossible or unwilling to upgrade the firmware, it may
> be possible to implement a compatibility layer and the booting procedure
> will be like:
>
> old firmware -> bootloongarch.efi -> customized u-boot -> bootloongarch64.efi (grub) -> efi stub (kernel)
>                  --------- compatibility layer --------    ^^^^^^^^ normal UEFI compatible stuff ^^^^^^^^^
>
> new firmware -> bootloongarch64.efi (grub) -> efi stub (kernel)
>
> The old firmware route would be similar to the booting procedure of
> Asahi Linux.  I think this can be implemented because it's already
> implemented on M1 even while Apple is almost completely uncooperative.

This is a bit off-topic (we're basically hurrying up to get the port 
into v5.19-rc1 and discussing ways to achieve that), but yeah 
definitely. I've had the same idea right after knowing the LoongArch 
firmware would also have "new-world" variant, then I contacted some 
firmware engineers working on LoongArch boards, I think they agreed on 
the approach overall.

However, making the kernel itself capable of booting on both BPI and 
new-world UEFI firmware flavors may have its merits after all; one 
scenario I could come up with is that user reboots and upgrades their 
firmware, *before* updating their old-world kernel, and bang! system 
soft-bricked. All such cases involve old-world distros that already 
deviate a little bit from vanilla upstream code, so such BPI support 
needn't be mainlined for avoiding this scenario.

> Just my 2 cents. I know almost nothing about booting.
That's fine, we all know nothing in the beginning ;-)