Re: [RFC PATCH] x86: Add safe_udelay() and safe_msleep()

[Yinghai Lu <yinghai@kernel.org>]

On 01/11/2011 06:32 PM, Benjamin Herrenschmidt wrote:
> On Tue, 2011-01-11 at 17:06 -0800, Yinghai Lu wrote:
>> We need to use those function in early-quirk stage with code that is shared with
>> later stage.
>>
>> for x86, normal udelay() will need to wait per_cpu(cpu_info) is allocated... that i
>> after smp_prepare_cpus(), because it need to use percpu.loops_per_jiffy.
>>
>> Also msleep() will need to wait schedular is ready.
>>
>> Try to have one early version udelay that use loops_per_jiffy directly.
>> and early msleep is just early delay.
>>
>> This patch will set safe_udelay to early in x86 early arch code, and then init/main.c
>> will set them back.
> 
> I still think it's better to just make msleep() work with and without
> scheduler and avoid having to bother with a new API

please check if you are happy with this one.

[PATCH] x86: Make udelay() and msleep() can be used early

We need to use those functions in early-quirk stage with code that is shared with
later stage.

For x86, normal udelay need to use percpu.loops_per_jiffy
will need to wait per_cpu(cpu_info) is allocated and copied
from boot_cpu_data, after it is in smp_prepare_cpus()
boot_cpu_data.loops_per_jiffy get set in identify_boot_cpu from check_bugs.

Also msleep() will need to wait schedular is ready.

Try to have one early version udelay that use loops_per_jiffy directly.
and early msleep is just early delay.

-v2: use function pointer and keep old udelay() and msleep() API as requested from BenH

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
 arch/x86/lib/delay.c  |   28 +++++++++++++++++++++++++++-
 include/linux/delay.h |    2 ++
 init/main.c           |    3 +++
 kernel/timer.c        |   28 +++++++++++++++++++++++-----
 4 files changed, 55 insertions(+), 6 deletions(-)

Index: linux-2.6/arch/x86/lib/delay.c
===================================================================
--- linux-2.6.orig/arch/x86/lib/delay.c
+++ linux-2.6/arch/x86/lib/delay.c
@@ -113,7 +113,7 @@ void __delay(unsigned long loops)
 }
 EXPORT_SYMBOL(__delay);
 
-inline void __const_udelay(unsigned long xloops)
+static void __normal_const_udelay(unsigned long xloops)
 {
 	int d0;
 
@@ -125,8 +125,34 @@ inline void __const_udelay(unsigned long
 
 	__delay(++xloops);
 }
+
+/* before percpu cpu_info.loops_per_jiffy is set */
+static void __init __early_const_udelay(unsigned long xloops)
+{
+	int d0;
+
+	xloops *= 4;
+	asm("mull %%edx"
+		: "=d" (xloops), "=&a" (d0)
+		: "1" (xloops), "0"
+		(loops_per_jiffy * (HZ/4)));
+
+	delay_loop(++xloops);
+}
+
+static void (*__const_udelay_fn)(unsigned long) = __early_const_udelay;
+
+void __const_udelay(unsigned long usecs)
+{
+	__const_udelay_fn(usecs);
+}
 EXPORT_SYMBOL(__const_udelay);
 
+void __init use_normal_delay(void)
+{
+	__const_udelay_fn = __normal_const_udelay;
+}
+
 void __udelay(unsigned long usecs)
 {
 	__const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
Index: linux-2.6/include/linux/delay.h
===================================================================
--- linux-2.6.orig/include/linux/delay.h
+++ linux-2.6/include/linux/delay.h
@@ -52,4 +52,6 @@ static inline void ssleep(unsigned int s
 	msleep(seconds * 1000);
 }
 
+extern void use_normal_delay(void);
+extern void use_normal_sleep(void);
 #endif /* defined(_LINUX_DELAY_H) */
Index: linux-2.6/init/main.c
===================================================================
--- linux-2.6.orig/init/main.c
+++ linux-2.6/init/main.c
@@ -879,6 +879,9 @@ static int __init kernel_init(void * unu
 	cad_pid = task_pid(current);
 
 	smp_prepare_cpus(setup_max_cpus);
+	/* set them back, x86 use it for early delay*/
+	use_normal_delay();
+	use_normal_sleep();
 
 	do_pre_smp_initcalls();
 	lockup_detector_init();
Index: linux-2.6/kernel/timer.c
===================================================================
--- linux-2.6.orig/kernel/timer.c
+++ linux-2.6/kernel/timer.c
@@ -1723,11 +1723,7 @@ void __init init_timers(void)
 	open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
 }
 
-/**
- * msleep - sleep safely even with waitqueue interruptions
- * @msecs: Time in milliseconds to sleep for
- */
-void msleep(unsigned int msecs)
+static void __normal_msleep(unsigned int msecs)
 {
 	unsigned long timeout = msecs_to_jiffies(msecs) + 1;
 
@@ -1735,6 +1731,28 @@ void msleep(unsigned int msecs)
 		timeout = schedule_timeout_uninterruptible(timeout);
 }
 
+static void __init __early_msleep(unsigned int msecs)
+{
+	mdelay(msecs);
+}
+
+static void (*msleep_fn)(unsigned int) = __early_msleep;
+
+void __init use_normal_sleep(void)
+{
+	msleep_fn = __normal_msleep;
+}
+
+void __init __weak use_normal_delay(void) { }
+
+/**
+ * msleep - sleep safely even with waitqueue interruptions
+ * @msecs: Time in milliseconds to sleep for
+ */
+void msleep(unsigned int msecs)
+{
+	msleep_fn(msecs);
+}
 EXPORT_SYMBOL(msleep);
 
 /**