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@xxxxxxx> --- 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 +#endifWhen 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)
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