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

[Thomas Zimmermann]

Hi Geert

Am 11.04.23 um 10:08 schrieb Geert Uytterhoeven:
> Hi Thomas,
>
> On Thu, Apr 6, 2023 at 4:30 PM Thomas Zimmermann <tzimmermann@xxxxxxx> 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@xxxxxxx>
>
> 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"?

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.

> > +{
> > +       vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
>
> Shouldn't this use the pgprot_val() wrapper?

No, I think. Grep'ing for vm_page_prot, I'm not seeing it being used in 
such assignments.

Best regards
Thomas

> > +}
> > +#endif
>
> Gr{oetje,eeting}s,
>
>                          Geert

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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