linux-kernel - Re: [PATCH v2 01/19] fbdev: Prepare generic architecture helpers

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Date:   Tue, 11 Apr 2023 10:08:47 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     arnd@...db.de, daniel.vetter@...ll.ch, deller@....de,
        javierm@...hat.com, gregkh@...uxfoundation.org,
        linux-arch@...r.kernel.org, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 01/19] fbdev: Prepare generic architecture helpers

Hi Thomas,

On Thu, Apr 6, 2023 at 4:30 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:
> Generic implementations of fb_pgprotect() and fb_is_primary_device()
> have been in the source code for a long time. Prepare the header file
> to make use of them.
>
> Improve the code by using an inline function for fb_pgprotect()
> and by removing include statements. The default mode set by
> fb_pgprotect() is now writecombine, which is what most platforms
> want.
>
> Symbols are protected by preprocessor guards. Architectures that
> provide a symbol need to define a preprocessor token of the same
> name and value. Otherwise the header file will provide a generic
> implementation. This pattern has been taken from <asm/io.h>.
>
> v2:
>         *  use writecombine mappings by default (Arnd)
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@...e.de>

Thanks for your patch!

> --- a/include/asm-generic/fb.h
> +++ b/include/asm-generic/fb.h
> @@ -1,13 +1,32 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
> +
>  #ifndef __ASM_GENERIC_FB_H_
>  #define __ASM_GENERIC_FB_H_
> -#include <linux/fb.h>
>
> -#define fb_pgprotect(...) do {} while (0)
> +/*
> + * Only include this header file from your architecture's <asm/fb.h>.
> + */
> +
> +#include <asm/page.h>
> +
> +struct fb_info;
> +struct file;
> +
> +#ifndef fb_pgprotect
> +#define fb_pgprotect fb_pgprotect
> +static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
> +                               unsigned long off)

Does this affect any noMMU platforms that relied on fb_pgprotect()
doing nothing before?
Perhaps the body below should be protected by "#ifdef CONFIG_MMU"?

> +{
> +       vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);

Shouldn't this use the pgprot_val() wrapper?

> +}
> +#endif

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds