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

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Date:   Mon, 17 Apr 2023 11:22:24 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Thomas Zimmermann" <tzimmermann@...e.de>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>
Cc:     "Daniel Vetter" <daniel.vetter@...ll.ch>,
        "Helge Deller" <deller@....de>,
        "Javier Martinez Canillas" <javierm@...hat.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Linux-Arch <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

On Mon, Apr 17, 2023, at 11:03, Thomas Zimmermann wrote:
> Am 11.04.23 um 10:08 schrieb Geert Uytterhoeven:
>> On Thu, Apr 6, 2023 at 4:30 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:

>>> +#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"?
>
> I cannot conclusively answer this question, but I did some grep'ing 
> ('git grep ndef | grep CONFIG_MMU'):
>
> Only the architectures in this patchset provide <asm/fb.h> but nothing 
> anywhere uses <asm-generic/fb.h> yet. And of those architectures, only 
> arm and m68k have !CONFIG_MMU cases. Those are handled in the rsp 
> patches. I think we're good.

Agreed. The generic version is just a more elaborate way to do
nothing here, as the 

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

line on nommu just turns into a self-assignment of the same member
that was set the line before.

     Arnd