Hi Am 28.04.23 um 15:17 schrieb Arnd Bergmann:
On Fri, Apr 28, 2023, at 13:27, Geert Uytterhoeven wrote:On Fri, Apr 28, 2023 at 2:18 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:On 2023-04-28 10:27, Thomas Zimmermann wrote:- -#elif defined(__i386__) || defined(__alpha__) || defined(__x86_64__) || \ - defined(__hppa__) || defined(__sh__) || defined(__powerpc__) || \ - defined(__arm__) || defined(__aarch64__) || defined(__mips__) - -#define fb_readb __raw_readb -#define fb_readw __raw_readw -#define fb_readl __raw_readl -#define fb_readq __raw_readq -#define fb_writeb __raw_writeb -#define fb_writew __raw_writew -#define fb_writel __raw_writel -#define fb_writeq __raw_writeqNote that on at least some architectures, the __raw variants are native-endian, whereas the regular accessors are explicitly little-endian, so there is a slight risk of inadvertently changing behaviour on big-endian systems (MIPS most likely, but a few old ARM platforms run BE as well).Also on m68k, when ISA or PCI are enabled. In addition, the non-raw variants may do some extras to guarantee ordering, which you do not need on a frame buffer. So I'd go for the __raw_*() variants everywhere.The only implementations in fbdev are 1) sparc sbus 2) __raw_writel 3) direct pointer dereference But none use the byte-swapping writel() implementations, and the only ones that use the direct pointer dereference or sbus are the ones on which these are defined the same as __raw_writel
After thinking a bit more about the requirements, I'd like to got back to v1, but with a different spin. We want to avoid ordering guarantees, so I looked at the _relaxed() helpers, but they seem to swap bytes to little endian.
I guess we can remove the fb_mem*() functions entirely. They are the same as the non-fb_ counterparts. For the fb read/write helpers, I'd like to add them to <asm-generic/fb.h> in a platform-neutral way. They'd be wrappers around __raw_(), as I wouldn't want invocations of __raw_() functions in the fbdev drivers.
Best regards Thomas
Arnd
-- 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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