[PATCHv5 2/3] ARM: Allow machines to override __delay()
sboyd at codeaurora.org
Tue Apr 5 19:56:39 EDT 2011
Some machines want to implement their own __delay() routine based
on fixed rate timers. Expose functionality to set the __delay()
routine at runtime. This should allow two machines with different
__delay() routines to happily co-exist within the same kernel
with minimal overhead.
Russell expressed concern that using a timer based __delay()
would cause problems when an iomapped device isn't mapped in
prior to a delay call being made (see
more info). We can sidestep that issue with this approach since
the __delay() routine _should_ only be pointed to a timer based
delay once the timer has been properly mapped. Up until that
point __delay() and udelay() will use delay_loop() which is
always safe to call.
This patch is inspired by x86's delay.c
Reviewed-by: Saravana Kannan <skannan at codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd at codeaurora.org>
arch/arm/include/asm/delay.h | 7 +++++++
arch/arm/lib/delay.c | 14 +++++++++++---
2 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
index ccc5ed5..82ef82a 100644
@@ -40,5 +40,12 @@ extern void __const_udelay(unsigned long);
__const_udelay((n) * ((2199023U*HZ)>>11))) : \
+extern void (*delay_fn)(unsigned long);
+static inline void set_delay_fn(void (*fn)(unsigned long))
+ delay_fn = fn;
#endif /* defined(_ARM_DELAY_H) */
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index daca2be..42cda15 100644
@@ -11,11 +11,9 @@
- * loops = usecs * HZ * loops_per_jiffy / 1000000
* Oh, if only we had a cycle counter...
-void __delay(unsigned long loops)
+static void delay_loop(unsigned long loops)
"1: subs %0, %0, #1 \n"
@@ -24,6 +22,16 @@ void __delay(unsigned long loops)
: "r" (loops)
+void (*delay_fn)(unsigned long) = delay_loop;
+ * loops = usecs * HZ * loops_per_jiffy / 1000000
+void __delay(unsigned long loops)
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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