linux-kernel - Re: [PATCH V11 09/22] LoongArch: Add boot and setup routines

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Message-ID: <cdbb002a-9f0a-caa9-445e-4ba20328171a@redhat.com>
Date:   Fri, 20 May 2022 16:23:07 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Huacai Chen <chenhuacai@...il.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH V11 09/22] LoongArch: Add boot and setup routines

Hello Huacai,

On 5/20/22 16:09, Huacai Chen wrote:

[snip]

>>
>> In summary, just enable the following to use the firmware framebuffer:
>>
>> CONFIG_DRM_SIMPLEDRM=y
>> CONFIG_DRM_FBDEV_EMULATION=y
>> CONFIG_SYSFB=y
>> CONFIG_SYSFB_SIMPLEFB=y
> Thank you very much, since 5.15 sysfb_init() do all things of
> register_gop_device(), so register_gop_device() here can be removed.

Correct.

> But there is another small problem: if simpledrm or efifb driver is
> built-in, there is no display. The reason is both sysfb_init() and
> display driver are in the same initcall level (device_initcall()).
> From the comments I know that sysfb_init() should after PCI
> enumeration which is in subsys_initcall(), so, could we make
> sysfb_init() to be a subsys_initcall_sync()?
>

I don't understand why we would need that... it shouldn't matter the order
in which the driver's init and sysfb_init() are done. If the driver's init
is executed first, then the driver will be registered and later when the
sysfb_init() registers the device, it will match the driver and probe.

Conversely, if the sysfb_init() is executed first then the platform device
will be registered and latter when the driver's init register the driver
this will match the already registered device.

In other words, it will be handled by the Linux device model and we should
not attempt to hand pick the initcall level for each. That's quite fragile.

Or am I missing something here ?

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat