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

[Sam Ravnborg <sam@ravnborg.org>]

Hi Thomas,

On Tue, May 02, 2023 at 03:02:21PM +0200, Thomas Zimmermann wrote:
> Fbdev's main header file, <linux/fb.h>, includes <asm/io.h> to get
> declarations for I/O helper functions. From these declarations, it
> later defines framebuffer I/O helpers, such as fb_{read,write}[bwlq]()
> or fb_memset().
> 
> The framebuffer I/O helpers depend on the system architecture and
> will therefore be moved into <asm/fb.h>. Prepare this change by first
> adding an include statement for <linux/io.h> to <asm-generic/fb.h>.
> Include <asm/fb.h> in all source files that use the framebuffer I/O
> helpers, so that they still get the necessary I/O functions.
> 
...
> 
> diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c
> index 60a96fdb5dd8..fd38e8a073b8 100644
> --- a/drivers/video/fbdev/arkfb.c
> +++ b/drivers/video/fbdev/arkfb.c
> @@ -27,6 +27,8 @@
>  #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.

	Sam