linux-kernel - Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80 on some AMD64x2 laptops, etc.

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Date:	Fri, 14 Dec 2007 15:56:55 +0100
From:	Rene Herman <rene.herman@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Rene Herman <rene.herman@...il.com>,
	"David P. Reed" <dpreed@...d.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80
 on some AMD64x2 laptops, etc.

On 14-12-07 15:46, Ingo Molnar wrote:

> * Rene Herman <rene.herman@...il.com> wrote:
> 
>>>>  /*
>>>> - * This should be approx 2 Bo*oMips to start (note initial shift), and will
>>>> - * still work even if initially too large, it will just take slightly longer
>>>> + * Initial value roughly corresponds to a 1 GHz CPU
>>>>   */
>>>> -unsigned long loops_per_jiffy = (1<<12);
>>>> +unsigned long loops_per_jiffy = 1000000000 / HZ;
>>>>
>>>>  EXPORT_SYMBOL(loops_per_jiffy);
>>> this is a factor of ~2400 increase - this will take an eternity to boot on 
>>> any older CPU.
>> Only any outb_p's used before loops_per_jiffy is calibrated are 
>> affected.
> 
> yes - but there are a couple of early udelays, which would thus be 
> affected.

True. At the moment though they're just always not delaying anywhere close 
the intended amount (on anything with more than 2 bogomips). Pre-calibration 
all this stuff is just broken it seems.

>> This pre-calibation thing is what's historically held this change back 
>> (it's been discussed dozens of times before). At 4096, not any machine 
>> is going to have an appreciable delay before calibration when 
>> switching from the outb to 0x80.
> 
> i dont think this should matter: old systems that truly _need_ the ISA 
> delay will be slow enough to not trip up. (nor are they really affected 
> by these early delays - the delays were more for crappy ISA devices that 
> get initialized later down, when the delay loop is already calibrated)

8253 (DMAC) and 8254 (PIT) have been reported in earlier versions of the 
thread. By Alan, I believe.

Rene.
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