linux-kernel - Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

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Date:	Mon, 17 Dec 2007 17:48:32 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"David P. Reed" <dpreed@...d.com>,
	Rene Herman <rene.herman@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Paul Rolland <rol@...917.net>,
	Pavel Machek <pavel@....cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	rol@...be.net
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> I don't think we should be offering udelay based delays at this point. 
> There are a lot of drivers to fix first. This is just one trivial 
> example
> 
> ...
> 
> --- drivers/watchdog/wdt.c~	2007-12-17 15:58:49.000000000 +0000
> +++ drivers/watchdog/wdt.c	2007-12-17 15:58:49.000000000 +0000
> @@ -70,6 +70,8 @@
>  static int io=0x240;
>  static int irq=11;
>  
> +static DEFINE_SPINLOCK(wdt_lock);
> +
>  module_param(io, int, 0);
>  MODULE_PARM_DESC(io, "WDT io port (default=0x240)");
>  module_param(irq, int, 0);
> @@ -109,6 +111,8 @@
>  
>  static int wdt_start(void)
>  {
> +	unsigned long flags;
> +	spin_lock_irqsave(&wdt_lock, flags);
>  	inb_p(WDT_DC);			/* Disable watchdog */
>  	wdt_ctr_mode(0,3);		/* Program CTR0 for Mode 3:

a really stupid question, in what way does:

  inb_p(WDT_DC);

work better than:

  inb(WDT_DC);
  delay(2);

?

(i'm not suggesting you are wrong, this detail just fails to click at 
the moment.)

	Ingo
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