Messages in this thread | | | Date | Sun, 17 Feb 2008 10:44:32 +0100 (CET) | From | Geert Uytterhoeven <> | Subject | Re: [Linux-fbdev-devel] [PATCH 1/2] fb: add support for foreign endianness |
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On Fri, 15 Feb 2008, Anton Vorontsov wrote: > On Thu, Feb 14, 2008 at 10:49:42PM -0800, Andrew Morton wrote: > > On Tue, 5 Feb 2008 18:44:32 +0300 Anton Vorontsov <avorontsov@ru.mvista.com> wrote: > > > This patch adds support for the framebuffers with non-native > > > endianness. This is done via FBINFO_FOREIGN_ENDIAN flag that will > > > be used by the drivers. Depending on the host endianness this flag > > > will be overwritten by FBINFO_BE_MATH internal flag, or cleared. > > > > > > Tested to work on MPC8360E-RDK (BE) + Fujitsu MINT framebuffer (LE). > > > > That's a pretty large patch to fbdev core, > > Yes, but changes are mostly trivial. No insurance of typos and thinkos > though. OTOH, it survived my tests. > > > and Tony appears to have gone > > offline again and you didn't cc the fbdev mailing list. > > FRAMEBUFFER LAYER > P: Antonino Daplas > M: adaplas@gmail.com > L: linux-fbdev-devel@lists.sourceforge.net (subscribers-only) > > I'm lazy to subscribe on occasional patches. Yup, this is hardly > an excuse...
While linux-fbdev is subscribers-only, non-subscribers are not plainly rejected, but moderated, so the casual patch/comment/question comes through.
I'll cook up a patch for MAINTAINERS to clarify.
> > Actually... should CONFIG_FB_FOREIGN_ENDIAN exist, or should this feature > > be permanently enabled? > > It should not. Because with CONFIG_FB_FOREIGN_ENDIAN enabled, drawing > might be a little bit slower, because of external checks for endianness > (I didn't noticed any slowdown, but I guess it's still measurable if we > find some fb benchmark).
> > I'd like to at least queue a patch in -mm so that CONFIG_FB_FOREIGN_ENDIAN > > is forced-on, so the code gets some runtime testing. Will that break > > anything? > > Nope, it should not break anything, just possible fbconsole/tux drawing > slowdown.
Tux drawing speed doesn't really matter, as it's done once only. Console text drawing is different.
`time cat MAINTAINERS' is a good test. Of course, is most time is spent in scrolling, you won't see much difference.
So probably we need a test file that contains lines of text interspersed with `HOME' escape sequences, so we don't scroll?
> Thinking about it a little bit more, I believe we want to add a choice, > which exactly foreign endianness we want to compile-in. Then, if we're > pretty confident that particular BE machine uses only LE framebuffer, > gcc can optimize away endianness checks. > > Patch on top of previous inlined here. With that patch, slowdown is > possible with CONFIG_FB_BOTH_ENDIAN option only, which is still > default if FOREIGN_ENDIAN is selected. > With this patch FB_FOREIGN_ENDIAN converted to menuconfig with the > choice inside: which type of foreign endianness we want to compile-in. >
The notion of `FOREIGN_ENDIAN' is relative, as it depends on the architecture you're compiling for.
Suppose you have a PCI graphics card with a frame buffer that's always big endian. When compiling for a big endian platform, the driver won't depend on FB_FOREIGN_ENDIAN. When compiling for a little endian platform, it will.
Shouldn't we add LITTLE_ENDIAN and BIG_ENDIAN Kconfig vars first, just like we have 64BIT?
> As a bonus, now fb subsystem will refuse to register framebuffer with > unsupported endianness, and will suggest a way to solve the problem.
I'd like to handle this in Kconfig (cfr. above).
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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