Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Message-ID: <f7b53d2b-759c-bc5b-e2ed-a251b879f450@xen0n.name>
Date:   Fri, 3 Jun 2022 17:48:05 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:103.0) Gecko/20100101
 Thunderbird/103.0a1
Subject: Re: Steps forward for the LoongArch UEFI bringup patch? (was: Re:
 [PATCH V14 11/24] LoongArch: Add boot and setup routines)
Content-Language: en-US
To:     Xi Ruoyao <xry111@xry111.site>, WANG Xuerui <kernel@xen0n.name>,
        Ard Biesheuvel <ardb@kernel.org>,
        Huacai Chen <chenhuacai@loongson.cn>
Cc:     linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Xuefeng Li <lixuefeng@loongson.cn>,
        Yanteng Si <siyanteng@loongson.cn>,
        Huacai Chen <chenhuacai@gmail.com>,
        Guo Ren <guoren@kernel.org>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        linux-efi@vger.kernel.org, WANG Xuerui <git@xen0n.name>,
        Yun Liu <liuyun@loongson.cn>, Jonathan Corbet <corbet@lwn.net>,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Airlie <airlied@linux.ie>,
        Linus Torvalds <torvalds@linux-foundation.org>
References: <20220602115141.3962749-1-chenhuacai@loongson.cn>
 <20220602115141.3962749-12-chenhuacai@loongson.cn>
 <d88ede74-b7a5-e568-1863-107c6c7f5fe0@xen0n.name>
 <dab96b787bef91240c719ea1a100396350135f99.camel@xry111.site>
From:   WANG Xuerui <kernel@xen0n.name>
In-Reply-To: <dab96b787bef91240c719ea1a100396350135f99.camel@xry111.site>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

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 ;-)