Woops, misspelling of kernel.org in the original email... ---------- Forwarded message ---------- From: Geert Uytterhoeven <[email protected]> Date: Fri, Dec 13, 2013 at 8:16 PM Subject: Re: [PATCH 3/4] arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h To: Peter Zijlstra <[email protected]> Cc: Linux-Arch <[email protected]>, [email protected], Paul McKenney <[email protected]>, Linus Torvalds <[email protected]>, Victor Kaplansky <[email protected]>, Oleg Nesterov <[email protected]>, Anton Blanchard <[email protected]>, Benjamin Herrenschmidt <[email protected]>, Frédéric Weisbecker <[email protected]>, Mathieu Desnoyers <[email protected]>, Michael Ellerman <[email protected]>, Michael Neuling <[email protected]>, Russell King <[email protected]>, Martin Schwidefsky <[email protected]>, Heiko Carstens <[email protected]>, Tony Luck <[email protected]>
Hi Peter, On Fri, Dec 13, 2013 at 3:57 PM, Peter Zijlstra <[email protected]> wrote: > There are a few architectures (m32r, m68k) that could probably > do away with their barrier.h file entirely but are kept for now due to > their unconventional nop() implementation. m32r uses `__asm__ __volatile__ ("nop" : : )' instead of `asm volatile ("nop")'. Isn't the latter just a shorthand of the former? m68k has an additional `barrier()', which I think is unneeded. I looked at the asm output for drivers/block/ataflop.c and drivers/video/macfb.c, with and without the barrier. For ataflop, there were no differences. For macfb, removing the barrier allowed the compiler to keep the base addresses of the MMIO registers in registers, but there were no changes to the register accesses themselves. So IMHO both m32r and m68k can switch to the asm-generic version. I'm wondering whether we can just drop nop() from the in-kernel API? There are few users outside arch/: drivers/block/ataflop.c drivers/net/ethernet/amd/am79c961a.c drivers/tty/serial/crisv10.c drivers/video/macfb.c >From a quick glance, all of them (ab)use nop() instead of one of the other primitives. For the macfb case, it seems to be due to missing ordering inside the nubus_*() I/O accessors. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected] 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 -- Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected] 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
