linux-kernel - Re: [PATCH v3 4/6] fbdev: Include <linux/io.h> via <asm/fb.h>

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Date:   Wed, 03 May 2023 09:19:21 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     linux-arch@...r.kernel.org, linux-fbdev@...r.kernel.org,
        linux-ia64@...r.kernel.org, loongarch@...ts.linux.dev,
        arnd@...db.de, deller@....de, chenhuacai@...nel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        James.Bottomley@...senpartnership.com,
        linux-m68k@...ts.linux-m68k.org, geert@...ux-m68k.org,
        linux-parisc@...r.kernel.org, vgupta@...nel.org,
        sparclinux@...r.kernel.org, kernel@...0n.name,
        linux-snps-arc@...ts.infradead.org, davem@...emloft.net,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 4/6] fbdev: Include <linux/io.h> via <asm/fb.h>

Thomas Zimmermann <tzimmermann@...e.de> writes:

Hello Thomas,

> Am 02.05.23 um 21:54 schrieb Sam Ravnborg:
>> On Tue, May 02, 2023 at 03:02:21PM +0200, Thomas Zimmermann wrote:

[...]

>>>   #include <linux/console.h> /* Why should fb driver call console functions? because console_lock() */
>>>   #include <video/vga.h>
>>>   
>>> +#include <asm/fb.h>
>> 
>> When we have a header like linux/fb.h - it is my understanding that it is
>> preferred to include that file, and not the asm/fb.h variant.
>> 
>> This is assuming the linux/fb.h contains the generic stuff, and includes
>> asm/fb.h for the architecture specific parts.
>> 
>> So drivers will include linux/fb.h and then they automatically get the
>> architecture specific parts from asm/fb.h.
>> 
>> In other words, drivers are not supposed to include asm/fb.h, if
>> linux.fb.h exists - and linux/fb.h shall include the asm/fb.h.
>> 
>> If the above holds true, then it is wrong and not needed to add asm/fb.h
>> as seen above.
>> 
>> 
>> There are countless examples where the above are not followed,
>> but to my best understanding the above it the preferred way to do it.
>
> Where did youher this? I only know about this in the case of asm/io.h 
> vs. linux/io.h.
>

I understand that's the case too. I believe even checkpatch.pl complains
about it? (not that the script always get right, but just as an example).

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat