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 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_writeq >>> >>> Note 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 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)