Messages in this thread | | | Date | Wed, 3 May 2023 08:58:49 +0200 | Subject | Re: [PATCH v3 5/6] fbdev: Move framebuffer I/O helpers into <asm/fb.h> | From | Thomas Zimmermann <> |
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Hi Sam
Am 02.05.23 um 22:03 schrieb Sam Ravnborg: > Hi Thomas, > > On Tue, May 02, 2023 at 03:02:22PM +0200, Thomas Zimmermann 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. > > In reality they are now all implemented in 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. > Which is also documented here.
The first paragraph documents the design intention, the other one the implementation. But I agree that it's not well phrased. I'll see if I can improve the text.
> >> >> v3: >> * implement all architectures with generic helpers >> * support reordering and native byte order (Geert, Arnd) >> >> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> >> --- >> include/asm-generic/fb.h | 101 +++++++++++++++++++++++++++++++++++++++ >> include/linux/fb.h | 53 -------------------- >> 2 files changed, 101 insertions(+), 53 deletions(-) >> >> diff --git a/include/asm-generic/fb.h b/include/asm-generic/fb.h >> index 6922dd248c51..0540eccdbeca 100644 >> --- a/include/asm-generic/fb.h >> +++ b/include/asm-generic/fb.h >> @@ -31,4 +31,105 @@ static inline int fb_is_primary_device(struct fb_info *info) >> } >> #endif >> >> +/* >> + * I/O helpers for the framebuffer. Prefer these functions over their >> + * regular counterparts. The regular I/O functions provide in-order >> + * access and swap bytes to/from little-endian ordering. Neither is >> + * required for framebuffers. Instead, the helpers read and write >> + * raw framebuffer data. Independent operations can be reordered for >> + * improved performance. >> + */ >> + >> +#ifndef fb_readb >> +static inline u8 fb_readb(const volatile void __iomem *addr) >> +{ >> + return __raw_readb(addr); >> +} >> +#define fb_readb fb_readb >> +#endif > > When we need to provide an architecture specific variant the > #ifndef foo > ... > #define foo foo > can be added. Right now it is just noise as no architectures provide > their own variants.
Given Arnd's comments, this might change. It also makes sense from a design POV.
> > But I am missing something somewhere as I cannot see how this builds. > asm-generic now provide the fb_read/fb_write helpers. > But for example sparc has an architecture specifc fb.h so it will not > use the asm-generic variant. So I wonder how sparc get hold of the > asm-generic fb.h file?
All architecture's <asm/fb.h> files include <asm-generic/fb.h>, so that they all get the interfaces which they don't define themselves. For Sparc, this is at [1].
Best regards Thomas
[1] https://cgit.freedesktop.org/drm/drm-tip/tree/arch/sparc/include/asm/fb.h#n19
> > Maybe it is obvious, but I miss it. > > 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) [unhandled content-type:application/pgp-signature] | |