Re: [PATCH v6 5/6] fbdev: Move framebuffer I/O helpers into <asm/fb.h>

[Thomas Zimmermann]

Hi Geert

Am 10.05.23 um 14:34 schrieb Geert Uytterhoeven:
> Hi Thomas,
>
> On Wed, May 10, 2023 at 1:06 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > Implement framebuffer I/O helpers, such as fb_read*() and fb_write*(),
> > in the architecture's <asm/fb.h> header file or the generic one.
> >
> > The common case has been the use of regular I/O functions, such as
> > __raw_readb() or memset_io(). A few architectures used plain system-
> > memory reads and writes. Sparc used helpers for its SBus.
> >
> > The architectures that used special cases provide the same code in
> > their __raw_*() I/O helpers. So the patch replaces this code with the
> > __raw_*() functions and moves it to <asm-generic/fb.h> for all
> > architectures.
> >
> > v6:
> >          * fix fb_readq()/fb_writeq() on 64-bit mips (kernel test robot)
> > v5:
> >          * include <linux/io.h> in <asm-generic/fb>; fix s390 build
> > v4:
> >          * ia64, loongarch, sparc64: add fb_mem*() to arch headers
> >            to keep current semantics (Arnd)
> > v3:
> >          * implement all architectures with generic helpers
> >          * support reordering and native byte order (Geert, Arnd)
> >
> > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Tested-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
> > Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > add mips fb_q()

Oops, left-over fom squashing patches.

> > --- a/arch/mips/include/asm/fb.h
> > +++ b/arch/mips/include/asm/fb.h
> > @@ -12,6 +12,28 @@ static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
> >   }
> >   #define fb_pgprotect fb_pgprotect
> >
> > +/*
> > + * MIPS doesn't define __raw_ I/O macros, so the helpers
> > + * in <asm-generic/fb.h> don't generate fb_readq() and
> > + * fb_write(). We have to provide them here.
>
> MIPS does not include <asm-generic/io.h>,  nor define its own

I know, that's why the TODO says to convert it to generic I/O.

> __raw_readq() and __raw_writeq()...

It doesn't define those macros, but it generates function calls of the 
same names. Follow the macros at


https://elixir.bootlin.com/linux/latest/source/arch/mips/include/asm/io.h#L357

It expands to a variety of helpers, including __raw_*().

> > + *
> > + * TODO: Convert MIPS to generic I/O. The helpers below can
> > + *       then be removed.
> > + */
> > +#ifdef CONFIG_64BIT
> > +static inline u64 fb_readq(const volatile void __iomem *addr)
> > +{
> > +       return __raw_readq(addr);
>
> ... so how can this call work?

On 64-bit builds, there's __raw_readq() and __raw_writeq().

At first, I tried to do the right thing and convert MIPS to work with 
<asm-generic/io.h>. But that created a ton of follow-up errors in other 
headers. So for now, it's better to handle this problem in asm/fb.h.

Best regards
Thomas

> > +}
> > +#define fb_readq fb_readq
> > +
> > +static inline void fb_writeq(u64 b, volatile void __iomem *addr)
> > +{
> > +       __raw_writeq(b, addr);
> > +}
> > +#define fb_writeq fb_writeq
> > +#endif
> > +
> >   #include <asm-generic/fb.h>
>
> Gr{oetje,eeting}s,
>
>                          Geert

--
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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