linux-kernel - Re: [PATCH v2 5/5] fbdev: Define framebuffer I/O from Linux' I/O functions

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Date:   Fri, 28 Apr 2023 15:12:21 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     deller@....de, geert@...ux-m68k.org, javierm@...hat.com,
        daniel@...ll.ch, vgupta@...nel.org, chenhuacai@...nel.org,
        kernel@...0n.name, davem@...emloft.net,
        James.Bottomley@...senpartnership.com, arnd@...db.de,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arch@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-parisc@...r.kernel.org
Subject: Re: [PATCH v2 5/5] fbdev: Define framebuffer I/O from Linux' I/O
 functions

Hi Thomas,

On Fri, Apr 28, 2023 at 11:27:11AM +0200, Thomas Zimmermann wrote:
> Implement framebuffer I/O helpers, such as fb_read*() and fb_write*()
> with Linux' regular I/O functions. Remove all ifdef cases for the
> various architectures.
> 
> Most of the supported architectures use __raw_() I/O functions or treat
> framebuffer memory like regular memory. This is also implemented by the
> architectures' I/O function, so we can use them instead.
> 
> Sparc uses SBus to connect to framebuffer devices. It provides respective
> implementations of the framebuffer I/O helpers. The involved sbus_()
> I/O helpers map to the same code as Sparc's regular I/O functions. As
> with other platforms, we can use those instead.
> 
> We leave a TODO item to replace all fb_() functions with their regular
> I/O counterparts throughout the fbdev drivers.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@...e.de>
> ---
>  include/linux/fb.h | 63 +++++++++++-----------------------------------
>  1 file changed, 15 insertions(+), 48 deletions(-)
> 
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 08cb47da71f8..4aa9e90edd17 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -15,7 +15,6 @@
>  #include <linux/list.h>
>  #include <linux/backlight.h>
>  #include <linux/slab.h>
> -#include <asm/io.h>
>  
>  struct vm_area_struct;
>  struct fb_info;
> @@ -511,58 +510,26 @@ struct fb_info {
>   */
>  #define STUPID_ACCELF_TEXT_SHIT
>  
> -// This will go away
> -#if defined(__sparc__)
> -
> -/* We map all of our framebuffers such that big-endian accesses
> - * are what we want, so the following is sufficient.
> +/*
> + * TODO: Update fbdev drivers to call the I/O helpers directly and
> + *       remove the fb_() tokens.
>   */
When the __raw_* variants are used, as Geert points out, then I think
the memcpy / memset can be replaced, but the rest seems fine to keep.

My personal opinion is that __raw_* is for macro use etc, and not
something to use everywhere. So I like the fb_read/fb_write macros.
But that is just my color of the bikeshed.

	Sam