On Thu, Jan 31, 2013 at 1:30 AM, Michael Schmitz <schmitzmic@xxxxxxxxx> wrote:
Signed-off-by: Michael Schmitz <schmitz@xxxxxxxxxx>
---
arch/m68k/include/asm/delay.h | 26 ++++++++++++++++++++++++++
1 files changed, 26 insertions(+), 0 deletions(-)
diff --git a/arch/m68k/include/asm/delay.h b/arch/m68k/include/asm/delay.h
index 12d8fe4..b18b667 100644
--- a/arch/m68k/include/asm/delay.h
+++ b/arch/m68k/include/asm/delay.h
@@ -92,5 +92,31 @@ static inline void __udelay(unsigned long usecs)
#define udelay(n) (__builtin_constant_p(n) ? \
((n) > 20000 ? __bad_udelay() : __const_udelay(n)) : __udelay(n))
+/*
+ * nanosecond delay:
+ *
+ * ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) is the number of loops per microsecond
+ *
+ * 1000 / ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) is the number of nanoseconds per loop
+ *
+ * So n / ( 1000 / ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) ) would be the number of loops for n nanoseconds
+ *
+ * ndelay(n) = __delay( DIV_ROUND_UP( (n) * ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6), 1000 ) )
This comment line is just a copy of the implementation?
+ */
+
+
+#if defined(CONFIG_M68000) || defined(CONFIG_COLDFIRE)
+/*
+ * The simpler m68k and ColdFire processors do not have a 32*32->64
+ * multiply instruction. So we need to handle them a little differently.
+ * We use a bit of shifting and a single 32*32->32 multiply to get close.
+ * This is a macro so that the const version can factor out the first
+ * multiply and shift.
+ */
+#define HZSCALE (268435456 / (1000000 / HZ))
+
+#define ndelay(n) __delay( DIV_ROUND_UP( (n) * ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6), 1000 ) );
+
+#endif
As both of CONFIG_M68000 and CONFIG_COLDFIRE are not set for regular Atari
builds, we still end up using the generic implementation in
<linux/delay.h>, which
does "udelay(DIV_ROUND_UP(x, 1000));"?
I.e. it will never wait for less than 1 us, do we really want that?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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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