linux-kernel - Re: [PATCH 0/5] fbdev: Move framebuffer I/O helpers to <asm/fb.h>

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Date:   Thu, 27 Apr 2023 09:22:47 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Sam Ravnborg <sam@...nborg.org>
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 0/5] fbdev: Move framebuffer I/O helpers to <asm/fb.h>

Hi Sam

Am 26.04.23 um 21:21 schrieb Sam Ravnborg:
> Hi Thomas.
> 
> On Wed, Apr 26, 2023 at 03:04:15PM +0200, Thomas Zimmermann wrote:
>> Fbdev provides helpers for framebuffer I/O, such as fb_readl(),
>> fb_writel() or fb_memcpy_to_fb(). The implementation of each helper
>> depends on the architecture. It's still all located in fbdev's main
>> header file <linux/fb.h>. Move all of it into each archtecture's
>> <asm/fb.h>, with shared code in <asm-generic/fb.h>.
> 
> For once I think this cleanup is moving things in the wrong direction.
> 
> The fb_* helpers predates the generic io.h support and try to
> add a generic layer for read read / write operations.
> 
> The right fix would be to migrate fb_* to use the io helpers
> we have today - so we use the existing way to handle the architecture
> specific details.

I looked through the existing versions of the fb_() I/O helpers. They 
can apparently be implemented with the regular helpers of similar names.

I'm not sure, but even Sparc looks compatible. At least these sbus_ 
functions seem to be equivalent to the __raw_() I/O helpers of similar 
names. Do you still have that Sparc emulator?

> 
>  From a quick look there seems to be some challenges but the current
> helpers that re-do part of io.h is not the way forward and hiding them
> in arch/include/asm/fb.h seems counter productive.

Which challenges did you see?

Best regards
Thomas

> 
> 	Sam

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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