linux-kernel - Re: [RFC PATCH] x86: Add safe_udelay() and safe

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Message-ID: <1294799565.9586.13.camel@pasglop>
Date:	Wed, 12 Jan 2011 13:32:45 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH] x86: Add safe_udelay() and safe_msleep()

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

Cheers,
Ben.

> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> 
> ---
>  arch/x86/include/asm/delay.h |    3 +++
>  arch/x86/kernel/setup.c      |    4 ++++
>  arch/x86/lib/delay.c         |   28 ++++++++++++++++++++++++++++
>  include/linux/delay.h        |    2 ++
>  init/main.c                  |    6 ++++++
>  5 files changed, 43 insertions(+)
> 
> Index: linux-2.6/arch/x86/include/asm/delay.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/delay.h
> +++ linux-2.6/arch/x86/include/asm/delay.h
> @@ -28,4 +28,7 @@ extern void __delay(unsigned long loops)
>  
>  void use_tsc_delay(void);
>  
> +extern void __early_udelay(unsigned long usecs);
> +extern void __early_msleep(unsigned int msecs);
> +
>  #endif /* _ASM_X86_DELAY_H */
> Index: linux-2.6/arch/x86/kernel/setup.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/setup.c
> +++ linux-2.6/arch/x86/kernel/setup.c
> @@ -853,6 +853,10 @@ void __init setup_arch(char **cmdline_p)
>  
>  	dmi_scan_machine();
>  
> +	/* for early using */
> +	safe_udelay = __early_udelay;
> +	safe_msleep = __early_msleep;
> +
>  	/*
>  	 * VMware detection requires dmi to be available, so this
>  	 * needs to be done after dmi_scan_machine, for the BP.
> 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
> @@ -138,3 +138,31 @@ void __ndelay(unsigned long nsecs)
>  	__const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
>  }
>  EXPORT_SYMBOL(__ndelay);
> +
> +/* before cpu_info.loops_per_jiffy get set */
> +static inline void __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);
> +}
> +
> +/* usecs need to < 2000 */
> +void __init __early_udelay(unsigned long usecs)
> +{
> +	/* 2**32 / 1000000 (rounded up) */
> +	__early_const_udelay(usecs * 0x000010c7);
> +}
> +
> +/* before schedular is there */
> +void __init __early_msleep(unsigned int msecs)
> +{
> +	while (msecs--)
> +		__early_udelay(1000);
> +}
> 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 (*safe_udelay)(unsigned long);
> +extern void (*safe_msleep)(unsigned int);
>  #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
> @@ -240,6 +240,9 @@ unsigned long loops_per_jiffy = (1<<12);
>  
>  EXPORT_SYMBOL(loops_per_jiffy);
>  
> +void (*safe_udelay)(unsigned long) = __udelay;
> +void (*safe_msleep)(unsigned int) = msleep;
> +
>  static int __init debug_kernel(char *str)
>  {
>  	console_loglevel = 10;
> @@ -879,6 +882,9 @@ 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*/
> +	safe_udelay = __udelay;
> +	safe_msleep = msleep;
>  
>  	do_pre_smp_initcalls();
>  	lockup_detector_init();


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